Morphological features and structure of flagellated protozoa. Morphology and biology of parasitic protozoa. Structure of a bacterial cell

The classification of protozoa has not yet been finally ordered. Until recently, all protozoa were combined into one type Protozoa, which was divided into 4 classes according to the methods of movement.

♣ Sarcode ( Sarcodina): these protozoa are capable of locomotion with the help of pseudopodia (pseudopodia), the shape of the body is inconsistent.

♣ Flagella ( Mastigophora): the shape of the body is constant, the organs of movement are flagella (one or more).

♣ Ciliates ( Infusoria): ciliate cells are covered with a large number of cilia, with which they move.

However, based on electron microscopy data, studies of origin, life cycles, biochemical, physiological and genetic features, it was found that protozoa do not have a common structural plan, and the differences between their classes are so great that they correspond to differences at the type level.

At present, all the simplest ( Protozoa) are separated into a separate kingdom Protista, which includes 7 types (International Committee on Protozoa, 1980). Representatives of three types are of medical importance:

Sarcomastigophora, Apicomplexa And Ciliophora. The classification of protozoa that are of medical importance is given below.

TYPE SARCOMASTIGOPHORA,

SUBTYPE SARCODINA(SARCODE)

dysenteric amoeba(lat. Entamoeba histolytica) - the causative agent of amoebiasis (amebic dysentery), anthroponosis. It was first described in 1875 by the Russian scientist F.A. Lesh. The disease is ubiquitous, especially in countries with tropical and subtropical climates.

Morphological features. There are 5 forms of dysenteric amoeba: a small vegetative form (translucent or forma minute), tissue form, large vegetative form ( form magna), precyst, and cyst.

The small vegetative form feeds on bacteria and undigested food residues in the human intestine. It is found in patients in remission or in carriers; it intensively multiplies by dividing in two, and also forms cysts. Cysts of the dysenteric amoeba are rounded, with a double thin membrane. A young cyst has one nucleus, which divides twice, resulting in a four-nucleus cyst.

In a weakened human body (with infection, hypothermia, etc.), a small vegetative form can turn into a pathogenic large vegetative form, which secretes a proteolytic enzyme that corrodes the intestinal wall with the formation of ulcers. It feeds on erythrocytes. This form is found in the feces of a patient in the acute period of the disease.

Life cycle. When it enters the human intestine, the dysenteric amoeba in most cases multiplies in the contents of the large intestine, without penetrating into the tissues and without causing intestinal dysfunction (the person is healthy, but serves as a cyst carrier). This form of dysenteric amoeba is called luminal ( forma minute). It moves with the help of pseudopodia. The nucleus is spherical, chromatin is located under the nuclear membrane in the form of small lumps; in the center of the nucleus is a small karyosome. In the large intestine, the luminal form is surrounded by a membrane and turns into a spherical cyst (about 12 microns in size) with 4 nuclei that do not differ in structure from the nucleus of the vegetative form; immature cysts contain 1–2 nuclei.

In the cytoplasm there is a vacuole with glycogen; some cysts contain special formations - chromatoid bodies. With faeces, cysts are released into the external environment and serve as a source of human infection. Cysts remain viable in water and moist soil for up to a month or more.

Diagram of the life cycle of the dysenteric amoeba.

1, 2 - cyst in the digestive tract.

3- metacystic amoeba when exiting the cyst.

4- small vegetative form (forma minuta)

5 - 10 - cysts, which are excreted with feces into the external environment.

11 - a large vegetative form (forma magna), found in the bloody-mucous secretions of the patient.

12 - pathogenic form (forma magna), tissue.

13,14- erythrophage.

In the human intestine, after the metacystic stage of development (dividing into 8 daughter amoebae), cysts give rise to luminal forms.

Development of amoebic dysentery. Sometimes the luminal form of the dysentery amoeba is introduced into the intestinal wall and multiplies there, forming ulcers (amebic dysentery). This form of dysenteric amoeba is called tissue. Ulcerative lesion of the large intestine is accompanied by the release of blood. Under these conditions, the luminal forms of dysenteric amoeba, as well as tissue forms that have entered the intestinal lumen from ulcers, increase in size up to 30 microns and acquire the ability to phagocytize erythrocytes. This form of dysenteric amoeba is called the large vegetative ( form magna) or erythrophage.

Getting into the external environment with faeces, form magna dies quickly. When the acute phase of the disease subsides, the large vegetative form decreases in size and passes into the luminal form, which then encysts in the intestine. Cysts released into the external environment serve as a source of infection.

The vegetative form of the dysenteric amoeba dies in the external environment within 15–20 minutes.

Invasive stage for humans- cyst.

Ways of human infection. The source of infection is the person who releases the cysts into the environment. A person becomes infected orally by swallowing the cysts along with contaminated water or food. Infection is possible through contaminated hands or through direct contact with a cyst carrier. Synanthropic flies (mechanical carrier) participate in the distribution of cysts.

The lumen of the large intestine, the walls of the large intestine. With blood flow, dysenteric amoebae can enter the liver, lungs, brain, skin, where they cause abscesses (amebiasis).

Intestinal amoebiasis is the most common form. Tissue forms of amoebae affect the intestinal walls, with the destruction of the intestinal mucosa and the formation of ulcers. This leads to intestinal bleeding, and amoebas begin to feed on red blood cells. Intestinal functions are disturbed, intoxication and anemia develop.

Extraintestinal forms of amebiasis. The most common form is amoebic liver abscess. Amoebic brain abscess occurs in less than 0.1% of cases of invasion. Clinical manifestations and prognosis depend on the size of the abscess and its location. Genitourinary amebiasis develops as a result of direct penetration of amoebae from the colon or with hematogenous drift.

Diagnostics. The diagnosis is made on the basis of the detection of large vegetative forms and cysts during microscopic examination of the fecal masses of patients or pus from abscesses of the affected organs. It should be remembered that non-pathogenic bacteria live in the human intestine. Entamoeba coli, whose cysts contain 8 nuclei, and in the cytoplasm of its vegetative form there are no erythrocytes.

Diagnosis of amoebic liver abscess can be difficult because its symptoms are often nonspecific. In this case, ultrasound and magnetic resonance imaging are performed.

Preventive actions. Identification and treatment of patients and carriers of cysts. Maintaining personal hygiene, protecting food from contamination, killing flies, protecting the environment from faecal contamination, boiling water, improving sanitation and hygiene conditions, and public health education. Because cysts survive in chlorinated water, iodine is used to disinfect drinking water. When visiting countries where the disease is widespread, you should eat only peeled fruits and vegetables and drink bottled water.

Life cycle. Circulation in nature of free-living forms of amoebas - water of ponds, lakes, swimming pools, moist soil, animal feces. Reservoirs for amoebas are humans and laboratory animals (mice and rabbits).

Ways of human infection. A person becomes infected through the nasopharynx with water during bathing and by airborne droplets by inhalation of dust with amoeba cysts. Amoeba Naegleria fowleri heat-loving, and an indirect reason for the increase in the incidence may be unusually hot weather in summer, as well as the general trend of global warming.

The structure of free-living pathogenic amoebas.

a - negleria: 1 - vegetative stage, 2 - flagellar stage, 3 - cyst;

b - acanthamoeba: 1 - vegetative stage, 2 - cyst.

Invasive stages- vegetative and cyst.

localization in the human body. Gray matter of the brain, cerebellum, olfactory nerve fibers, cornea of ​​the eye.

Action on the human body. Symptoms of the disease are associated with lesions of the central nervous system. The first symptoms of the disease can be headache, changes in taste and smell, vomiting. The person may then feel convulsions and even fall into a coma. Death usually occurs 3 to 7 days after the onset of the first symptoms.

Acanthamoeba is the causative agent of keratitis, a severe inflammation of the cornea of ​​the eye. Sometimes it is found on the human cornea with prolonged wearing of contact lenses.

The protozoan phylum includes approximately 25 thousand species of unicellular animals living in water, soil, or organisms of other animals and humans. Having a morphological similarity in the structure of cells with multicellular organisms, the protozoa differ significantly from them in functional terms.

If the cells of a multicellular animal perform special functions, then the cell of the simplest is an independent organism capable of metabolism, irritability, movement and reproduction.

The simplest are organisms at the cellular level of organization. Morphologically, the protozoan is equivalent to a cell, but physiologically it is a whole independent organism. The vast majority of them are microscopically small in size (from 2 to 150 microns). However, some of the living protozoa reach 1 cm, and the shells of a number of fossil rhizopods are up to 5-6 cm in diameter. The total number of known species exceeds 25 thousand.

The structure of the protozoa is extremely diverse, but they all have features characteristic of the organization and function of the cell. Common in the structure in the structure of protozoa are the two main components of the body - the cytoplasm and the nucleus.

cytoplasm

The cytoplasm is bounded by an outer membrane that regulates the flow of substances into the cell. In many protozoa, it is complicated by additional structures that increase the thickness and mechanical strength of the outer layer. Thus, formations such as pellicles and shells arise.

The cytoplasm of protozoa usually breaks up into 2 layers - the outer one is lighter and denser - ectoplasm and internal, equipped with numerous inclusions, - endoplasm.

General cellular organelles are localized in the cytoplasm. In addition, a variety of special organelles may be present in the cytoplasm of many protozoa. Various fibrillar formations are especially widespread - supporting and contractile fibers, contractile vacuoles, digestive vacuoles, etc.

Core

The simplest have a typical cell nucleus, one or more. The nucleus of protozoa has a typical two-layer nuclear membrane. Chromatin material and nucleoli are distributed in the nucleus. The nuclei of protozoa are characterized by exceptional morphological diversity in terms of size, number of nucleoli, amount of nuclear juice, etc.

Features of the vital activity of protozoa

Unlike somatic cells, multicellular protozoa are characterized by the presence of a life cycle. It is composed of a series of successive stages, which are repeated in the existence of each species with a certain regularity.

Most often, the cycle begins with the stage of the zygote, which corresponds to the fertilized egg of multicellular organisms. This stage is followed by singly or repeatedly repeated asexual reproduction, carried out by cell division. Then sex cells (gametes) are formed, the pairwise fusion of which again gives a zygote.

An important biological feature of many protozoa is the ability to encystment. At the same time, the animals round out, shed or draw in the organelles of movement, secrete a dense shell on their surface, and fall into a state of rest. In the encysted state, protozoa can tolerate drastic environmental changes while remaining viable. When conditions favorable for life return, the cysts open and the protozoa emerge from them in the form of active, mobile individuals.

According to the structure of the organelles of movement and the characteristics of reproduction, the protozoan type is divided into 6 classes. The main 4 classes are Sarcodaceae, Flagellates, Sporozoans and Ciliates.

Protozoa- eukaryotic unicellular microorganisms that make up the sub-kingdom Protozoa of the animal kingdom (Animalia). The protozoa include 7 types, of which four types (Sarcomastigophora, Apicomplexa, Ciliophora, Microspora) have representatives that cause diseases in humans. Dimensions protozoa fluctuate on average from 5 to 30 microns.

Outside, the protozoa are surrounded membrane (pellicle) - an analogue of the cytoplasmic membrane of animal cells. Some protozoa have supporting fibrils.

cytoplasm and nucleus correspond in structure to eukaryotic cells: the cytoplasm consists of the endoplasmic reticulum, mitochondria, lysosomes, numerous ribosomes, etc.; the nucleus has a nucleolus and a nuclear envelope.

Protozoa move by means of flagella, cilia and by the formation of pseudopodia.

Protozoa can eat as a result of phagocytosis or the formation of special structures. Many protozoa form cysts under adverse conditions - resting stages that are resistant to changes in temperature, humidity, etc.

Protozoa are stained according to Romanovsky-Giemsa (nucleus - red, cytoplasm - blue).

To subphylum Sarcodina

Type Apicomplexa. In the class Sporozoa (sporozoa), pathogenic representatives are the causative agents of toxoplasmosis, coccidiosis, sarcocystosis and malaria. The life cycle of malaria pathogens is characterized by alternating sexual reproduction (in the body of Anopheles mosquitoes) and asexual reproduction (in human tissue cells and erythrocytes they multiply by multiple division). Toxoplasma are shaped like crescents. Toxoplasmosis is transmitted to humans from animals. Toxoplasma can be transmitted through the placenta and affect the central nervous system and eyes of the fetus.

Phylum Ciliophora. The pathogenic representative - the causative agent of balantidiasis - affects the human large intestine. Balantidia have numerous cilia and are therefore mobile.

Classification ... The simplest are represented by 7 types, of which four types (Sarcomastigophora, Apicomplexa, Ciliopkora, Microspora) include pathogens in humans.

To subphylum Sarcodina(sarcodal) refers to dysenteric amoeba - the causative agent of human amoebic dysentery. Morphologically similar to it is a non-pathogenic intestinal amoeba. These protozoa move by forming pseudopodia. Nutrients are captured and immersed in the cytoplasm of cells. There is no sexual reproduction in amoebas. Under adverse conditions, they form a cyst.

Type Apicomplexa.In class Sporozoa(sporozoans) pathogenic representatives are the causative agents of toxoplasmosis, coccidiosis, sarcocystosis and malaria. The life cycle of malaria pathogens is characterized by alternating sexual reproduction (in the body of Anopheles mosquitoes) and asexual reproduction (in human tissue cells and erythrocytes they multiply by multiple division). Toxoplasma are shaped like crescents. Toxoplasmosis is transmitted to humans from animals. Toxoplasma can be transmitted through the placenta and affect the central nervous system and eyes of the fetus.

Type Ciliophora. The pathogenic representative - the causative agent of balantidiasis - affects the human large intestine. Balantidia have numerous cilia and are therefore mobile.

2.Agglutination reaction. Components, mechanism, methods of setting. Application.

Agglutination reaction- a simple reaction in which antibodies bind corpuscular antigens (bacteria, erythrocytes or other cells, insoluble particles with antigens adsorbed on them, as well as macromolecular aggregates). It occurs in the presence of electrolytes, for example, when an isotonic sodium chloride solution is added.

Apply various variants of the agglutination reaction: expanded, approximate, indirect, etc. The agglutination reaction is manifested by the formation of flakes or sediment (cells “glued” by antibodies that have two or more antigen-binding centers - Fig. 13.1). RA is used for:

1) antibody detection in the blood serum of patients, for example, with brucellosis (Wright, Heddelson reactions), typhoid fever and paratyphoid fever (Vidal reaction) and other infectious diseases;

2) pathogen definitions isolated from the patient;

3) determination of blood groups using monoclonal antibodies against erythrocyte allo-antigens.

To determine the patient's antibodies put a detailed agglutination reaction: a diagnosticum (suspension of killed microbes) is added to the dilutions of the patient's blood serum, and after several hours of incubation at 37 ° C, the highest dilution of the serum (serum titer) is noted, at which agglutination occurred, i.e. a precipitate formed.

The nature and rate of agglutination depend on the type of antigen and antibodies. An example is the features of the interaction of diagnosticums (O- and H-antigens) with specific antibodies. The agglutination reaction with O-diagnosticum (bacteria killed by heating, retaining a thermostable O-antigen) occurs in the form of fine-grained agglutination. The agglutination reaction with H-diagnosticum (bacteria killed by formalin, retaining the heat-labile flagellar H-antigen) is coarse-grained and proceeds faster.

If it is necessary to determine the pathogen isolated from the patient, put orienting agglutination reaction, using diagnostic antibodies (agglutinating serum), i.e., serotyping of the pathogen is carried out. An approximate reaction is carried out on a glass slide. To a drop of diagnostic agglutinating serum in a dilution of 1:10 or 1:20 add a pure culture of the pathogen isolated from the patient. A control is placed nearby: instead of serum, a drop of sodium chloride solution is applied. When a flocculent sediment appears in a drop with serum and microbes, a detailed agglutination reaction is performed in test tubes with increasing dilutions of agglutinating serum, to which 2-3 drops of the pathogen suspension are added. Agglutination is taken into account by the amount of sediment and the degree of clarification of the liquid. The reaction is considered positive if agglutination is noted in a dilution close to the titer of the diagnostic serum. At the same time, controls are taken into account: serum diluted with isotonic sodium chloride solution should be transparent, a suspension of microbes in the same solution should be uniformly turbid, without sediment.

Different related bacteria can be agglutinated by the same diagnostic agglutinating serum, making their identification difficult. Therefore, adsorbed agglutinating sera are used, from which cross-reacting antibodies have been removed by adsorption by their related bacteria. In such sera, antibodies specific only to this bacterium remain.

3.Causative agents of hepatitis B, C, D. Taxonomy. Feature. Carrying. Laboratory diagnostics. specific prophylaxis.

Hepatitis B virus - family Hepadnaviridae genus Orthohepadnavirus .

Morphology: DNA-containing spherical-shaped virus. It consists of a core consisting of 180 protein particles that make up the core HBs antigen and a lipid-containing shell containing the surface HBs antigen. Inside the core are DNA, the enzyme DNA polymerase, which has reversetase activity, and the terminal protein HBe antigen.

The genome is represented by double-stranded DNA in a circular shape.

cultural properties. It is not cultivated on chicken embryos, does not have hemolytic and hemagglutinating activity. HBV is cultivated only in cell culture.

resistance. High to environmental factors and disinfectants. The virus is resistant to prolonged exposure to an acidic environment, UV radiation, the action of alcohol, phenol.

Antigenic structure. Complicated. The supercapsid of the virus contains the HBs antigen, which is localized in the hydrophilic layer on the surface of the virion. 3 polypeptides in glycosylated form are involved in the formation of the HBs antigen: preSl - large polypeptide; preS2 - middle polypeptide; S is a small polypeptide.

Epidemiology: The development of an infectious process when it enters the blood. Infection occurs during parenteral manipulations (injections, surgical interventions), blood transfusion.

Pathogenesis and clinic of the disease. The incubation period is 3-6 months. The infectious process occurs after the penetration of the virus into the blood. HBV from the blood by endocytosis penetrates into the hepatocyte. After the penetration of the virus, the DNA plus-strand is completed by DNA polymerase to a full-fledged structure. The clinical picture is characterized by symptoms of liver damage, in most cases accompanied by the development of jaundice.

Immunity. Humoral immunity, represented by antibodies to the HBs antigen, protects hepatocytes from the virus, eliminating it from the blood.

Cellular immunity frees the body from infected hepatocytes due to the cytolytic function of T-killers. The transition from an acute form to a chronic one is provided by a violation of T-cell immunity.

Microbiological diagnostics. Use the serological method and PCR. Using ELISA and RNGA methods, hepatitis B markers are determined in the blood: antigens and antibodies. PCR determines the presence of viral DNA in blood and liver biopsies. Acute hepatitis is characterized by the detection of HBs antigen, HBe antigen and anti-HBc-IgM antibodies.

Treatment. Use of interferon, interferonogens: viferon, amixin, DNA polymerase inhibitor, adenine ribonoside drug.

Prevention. Exclusion of the virus from entering during parenteral manipulations and blood transfusions (using disposable syringes, testing for hepatitis B by the presence of the HBs antigen in the blood of blood donors).

Specific prophylaxis is carried out by vaccination with a recombinant genetically engineered vaccine containing the HBs antigen. All newborns are subject to vaccination in the first 24 hours of life. The duration of post-vaccination immunity is at least 7 years.

Hepatitis C virus belongs to the family Flaviviridae kind hepacivirus.

Morphology. A complexly organized RNA-containing virus of a spherical shape. The genome is represented by a single linear "+" RNA strand and has great variability.

Antigenic structure. The virus has a complex antigenic structure. The antigens are:

1. Envelope glycoproteins

2. Core antigen Hcc antigen

3. Non-structural proteins.

cultural properties. HCV is not cultivated on chicken embryos, does not have hemolytic and hemagglutinating activity. resistance. sensitive to ether, UV rays, heating up to 50C.

Epidemiology. HCV infection is similar to HBV infection. Most often, HCV is transmitted through blood transfusions, transplacental, sexual contact.

Clinic: Often there are anicteric forms, the course of infection in an acute form, in 50% of cases the process becomes chronic with the development of cirrhosis and primary liver cancer.

Microbiological diagnostics: PCR and serological testing are used. Confirmation of an active infectious process is the detection of PCR viral RNA in the blood. Serological testing is aimed at the detection of antibodies to NS3 by ELISA.

Prevention and treatment. For prevention - the same as for hepatitis B. Interferon and ribovirin are used for treatment. Specific prevention - no.

Hepatitis D virus - defective virus that does not have its own shell. The virion has a spherical shape, which consists of a single-stranded RNA and a core HDc antigen. These proteins regulate the synthesis of the virus genome: one protein stimulates the synthesis of the genome, the other inhibits it. There are three genotypes of the virus. All genotypes belong to the same serotype.

The reservoir of BFD in nature is HBV carriers. BFD infection is similar to HBV infection.

Microbiological diagnostics carried out by the serological method by determining antibodies to BFD by ELISA.

Prevention: all those measures that are used to prevent hepatitis B. Interferon preparations are used for treatment. The hepatitis B vaccine also protects against hepatitis D.

Ticket 3

Morphology of mushrooms

Mushrooms belong to the kingdom Fungi (Mycetes, Mycota). These are multicellular or unicellular non-photosynthetic (chlorophyll-free) eukaryotic microorganisms with a cell wall.

Mushrooms have a nucleus with a nuclear envelope, a cytoplasm with organelles, a cytoplasmic membrane and a multilayer, rigid cell wall consisting of several types of polysaccharides, as well as protein, lipids, etc. Some fungi form a capsule. The cytoplasmic membrane contains glycoproteins, phospholipids and ergosterols. Fungi are gram-positive microbes, vegetative cells are non-acid-resistant.

Mushrooms consist from long thin threads (hyphae) woven into a mycelium, or mycelium. Hyphae of lower fungi - phycomycetes - do not have partitions. In higher fungi - eumycetes - hyphae are separated by partitions; their mycelium is multicellular.

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

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Test

Morphology and systematics of protozoa

Performed

student of group 203b

Petrenko L.A.

checked

cand. honey. Sciences Stepansky D.O.

Introduction

The protozoa are eukaryotic unicellular microorganism belonging to the kingdom Protozoa sub-kingdom Animalia, which includes 7 types. Representatives of three of them Sarcomastigophora, Apicomplexa, Ciliophora cause diseases in humans. Pathogenic protozoa - pathogens of human diseases - include dysentery amoeba, Giardia, Trichomonas, Leishmania, Trypanosomes, Plasmodium malaria, Toxoplasma, Balantidia.

Many of these microorganisms were discovered in the second half of the 19th century. and pretty well researched. This primarily concerns morphology and structure. However, some issues related to genetics, antigenic structure and its variability, immunology of diseases caused by them, etc., remained poorly developed. This also applies to the problem of pathogenicity factors, specific prophylaxis and the search for new chemotherapeutic drugs.

1. Characteristics of protozoa

The cells of the protozoa are covered with a dense elastic membrane - the pellicle, formed by the peripheral layer of the cytoplasm. Some of them are provided with supporting fibrils and a mineral backbone that bacteria do not have. The cytoplasm of protozoa contains a compact nucleus or several nuclei surrounded by a membrane, nuclear juice (karyolymph), chromosomes and nucleoli, as well as structures characteristic of the cells of multicellular animal organisms: endoplasmic reticulum, ribosomes, mitochondria, Golgi apparatus, lysosomes, various types of vacuoles, etc.

The simplest have: organs of movement (flagella, cilia, pseudopodia), nutrition (digestive vacuoles) and excretion (contractile vacuoles); can feed as a result of phagocytosis or the formation of special structures. Some protozoa have supporting fibrils. They reproduce asexually - by double division or multiple division (schizogony), and some sexually (sporogony). Many of them form cysts under adverse conditions - resting stages that are resistant to changes in temperature, humidity, etc. When stained according to Romanovsky-Giemsa, the nucleus of the protozoa is stained red, and the cytoplasm is blue.

According to the type of nutrition, they can be heterotrophs or autotrophs. Many protozoa (dysenteric amoeba, giardia, trichomonads, leishmania, balantidia) can grow on nutrient media containing native proteins and amino acids. Cell cultures, chicken embryos and laboratory animals are also used for their cultivation.

Most of them have a heterotrophic type of metabolism. In simply organized forms, food capture occurs through phagocytosis. Protozoa, with more complex morphology, have special structures that allow them to absorb food. Respiration is carried out by the entire surface of the cell.

Most protozoa have 1 nucleus, but there are also multi-nuclear forms.

In the life cycle of most protozoa, the trophozoite stage is distinguished - an actively feeding and moving form, and the cyst stage. Cyst - a motionless form of the life cycle of protozoa, covered with a dense membrane and characterized by a sharply slowed down metabolism.

2. Classification of protozoa

Of medical importance are the simplest related classes:

Sarcode;

flagella;

spores;

ciliates.

3. Characteristics of the class

Sarcode:

Representatives of the Sarcode class (Sarcodina) are the most primitive protozoa. Their body shape is inconsistent.

They move with the help of pseudopods. They live in fresh water, in the soil, in the seas.

Flagella:

The body of the flagellates, in addition to the cytoplasmic membrane, is also covered with a pellicle - a special shell that ensures the constancy of their shape. There are one or more flagella, organelles of movement, which are thread-like outgrowths of ectoplasm. Inside the flagella are fibrils of contractile proteins. Some flagellates also have an undulating membrane - a kind of organelle of movement, which is based on the same flagellum, which does not protrude freely outside the cell, but passes along the outer edge of a long flattened outgrowth of the cytoplasm. The flagellum causes the undulating membrane to undulate. The base of the flagellum is always associated with the kinetosome, an organelle that performs energy functions. A number of flagellates also have a supporting organelle - an axostyle - in the form of a dense strand passing inside the cell.

Sporozoans:

Two variants of development cycles of sporozoans are characteristic:

The first version of the development cycle includes the stages of asexual reproduction: the sexual process in the form of copulation and sporogony. Asexual reproduction is carried out by simple and multiple division - schizogony. The sexual process is preceded by the formation of germ cells - male and female gametes. Gametes merge, and the resulting zygote is covered with a membrane, under which sporogony occurs - multiple division with the formation of sporozoites. Sporozoans with this type of life cycle live in the tissues of the internal environment.

The second variant of the development cycle is found in sporozoa living in cavity organs communicating with the external environment. It is very simple and includes the cyst and trophozoite stages.

Commensalism is a form of symbiosis in which one species uses the leftovers or surplus food of another without causing visible harm, but without bringing any benefit.

ciliates:

Ciliates are characterized by a constant body shape and the presence of a pellicle. Movement organelles are numerous cilia that cover the entire body and are polymerized flagella. Ciliates usually have 2 nuclei: a large one - the macronucleus, which regulates metabolism, and a small one - the micronucleus, which serves to exchange hereditary information during conjugation. The digestive apparatus is difficult to organize. There is a permanent formation: cytostome - cellular mouth, cytopharynx - cellular pharynx. Digestive vacuoles move through the endoplasm, while lytic enzymes are secreted in stages. This ensures complete digestion of food particles. Undigested food residues are ejected through the powder - a specialized area of ​​the cell surface.

4. Protozoa living in abdominal organs communicating with the external environment

The following groups of protozoa are distinguished:

Protozoa that live in the small intestine.

Protozoa that live in the large intestine.

Protozoa that live in abdominal organs.

Protozoa that live in the lungs.

Protozoa that live in the oral cavity.

Mouth amoeba (Entamoeba gingivalis) - class "Sarcode" - commensal living on the gums, plaque and in the crypts of the palatine tonsils in more than 25% of healthy people. Cell size is 6-30 microns, pseudopodia are wide. It feeds on bacteria and leukocytes; when bleeding from the gums, it can also capture erythrocytes. Cyst does not form.

Oral Trichomonas (Trihomonas tenax) - class "Flagellates" - commensal. Body shape pear-shaped, length 6-13 microns. At the anterior end there are 4 flagella, on the side there is an undulating membrane about ¼ of the body length long. It occurs in 30% of healthy people, and in adults more often than in children. It lives in the folds of the oral mucosa, cavities of the teeth, crypts of the tonsils in chronic tonsillitis, and with low acidity of gastric juice, it is also found in the stomach. Cyst does not form. Transmission from person to person of both types of oral Trichomonas occurs when kissing, using shared utensils and toothbrushes, as well as with droplets of saliva and sputum when sneezing and coughing.

5. Protozoa that live in the small intestine

The source of infection is only a person infested with Giardia. Giardia cysts are excreted in the feces and can persist in the external environment for a long time. In moist feces, they last up to 3 weeks, and in water - up to 2 months, they are resistant to chlorine. Ingestion with water from several to 10 cysts already leads to the development of invasion in humans. Transmission can also be carried out through food products, on which Giardia cysts remain viable from 6 hours to 2 days.

Transmission from person to person is also possible. In preschool institutions, the prevalence of lamblia is much higher than among adults.

For the development of giardiasis, it is enough to swallow several (up to 10) cysts. In the host's body, they multiply in huge quantities (up to 1 million Giardia and more can be found per 1 sq. cm of the intestinal mucosa). Persons infested with Giardia can excrete up to 18 billion cysts with feces during the day. Against the background of Giardia, increased reproduction of bacteria and yeast cells can be observed. This can lead to dysfunction of the biliary tract and pancreas.

Clinical manifestations - due to the deterioration of absorption, especially fats and carbohydrates. The activity of enzymes decreases, the absorption of vitamin B12 decreases, C-vitamin metabolism is disturbed.

Giardia cannot exist in the biliary tract (bile kills them). In this regard, Giardia cannot be the cause of severe disorders in the liver, cholecystocholangitis, and lesions of the nervous system.

Often there are combinations of lamblia carriage, with any diseases. The combination of lamblia with shigella causes more prolonged intestinal disorders, impaired immunogenesis and contributes to the transition of dysentery into chronic forms.

In most of the invaded giardiasis proceeds latently.

Laboratory diagnostics is carried out by microscopic examination of native and treated with Lugol's solution preparations prepared from feces and duodenal contents.

Prevention: personal hygiene

6. Protozoa that live in the large intestine

Most of the protozoa that live in the mucus covering the epithelium of the crypts are commensals. Two types of protozoa - dysentery amoeba and balantidia - are pathogenic, but in the body of a healthy person they can lead a commensal lifestyle for a long time.

Dysenteric amoeba (Entamoeba histolica) - the class "Sarcode" - the causative agent of amoebiasis.

The causative agent can exist in three forms:

tissue form;

vegetative form;

in the form of a cyst;

A large vegetative form (tissue form, erythrophage, hematophage) has a diameter of 20-30 microns, and with active movement it reaches a length of up to 60-80 microns. This form is able to phagocytize erythrocytes. Their number reaches 20 or more in one amoeba. It occurs only in sick people.

The translucent form (small vegetative form, free, non-tissue, pre-cystic) has a diameter of 15-20 microns. Erythrocytes do not phagocytize. Found in amoeba carriers.

The cyst stage is a formation with a diameter of 7-18 microns, has from 1 to 4 nuclei, is stable in the external environment.

Laboratory diagnostics. A microscopic examination of native preparations from the affected tissues, as well as from the feces of a patient with acute amoebiasis, is carried out.

Prevention: observance of rules of personal hygiene.

Balantidia (Balantidium coli) - the class "Ciliates" - the causative agent of balantidiasis.

This is a large protozoan, up to 200 microns long. The whole body is covered with cilia, there are cytostome and cytopharynx. Under the pellicle is a layer of transparent ectoplasm, deeper is the endoplasm with organelles and 2 nuclei. The macronucleus is dumbbell-shaped or bean-shaped, next to it is a small micronucleus. Balantidia cyst is oval, up to 50-60 microns. in diameter, covered with a two-layer membrane, has no cilia, a contractile vacuole is clearly distinguished in the cytoplasm.

It can live in the human intestine, feeding on bacteria and not harming it, but sometimes it penetrates the intestinal wall, causing the formation of ulcers with purulent and bloody discharge.

The disease is characterized by prolonged diarrhea with blood and pus, and sometimes perforation of the intestinal wall with peritonitis. It can also enter the bloodstream and settle in the liver, lungs and other organs, causing the formation of abscesses there.

In addition to humans, balantidia is also found in rats and pigs, which are its main reservoir.

Laboratory diagnostics. Conduct a microscopic examination of fresh (native) preparations of feces of sick people, in which large, well-moving balantidia are easily detected.

Dientamoeba fragilis - coexists in a kind of symbiosis with pinworms. It does not form cysts, and trophozoites attach to pinworm eggs, through which infection of new hosts occurs. Reproducing in large numbers in the human intestine, this amoeba can cause short-term diarrhea.

The well-known flagellate, intestinal Trichomonas (Trihomonas hominis), has the same medical significance.

7. Protozoa that live in the genitals

Trichomonas vaginalis (Tnchamonas vaginalis) - class "Flagellates" - the causative agent of trichomoniasis.

Cyst does not form. This Trichomonas lives in women in the vagina and cervix, and in men - in the urethra, bladder and prostate gland. It causes the appearance of small inflammatory foci under the epithelial layer and desquamation of the surface cells of the mucous membrane. Leukocytes enter the lumen of the organ through the disturbed epithelial lining. In men, the disease usually resolves spontaneously after about 1 month. In women, trichomoniasis can occur for several years.

Prevention - compliance with the rules of personal hygiene during sexual intercourse.

8. Protozoa that live in the lungs

Recently, thanks to molecular biology, data have appeared that have allowed some researchers to attribute P. Carinii to fungi.

The pneumocyst has a thin capsule, can be round or sickle-shaped. It can be mistaken for yeast or erythrocytes under light microscopy.

Trophozoites have an irregular oval shape, their sizes are from 1 to 5 microns. Their cytoplasm contains mitochondria, and dissimilation occurs aerobically.

In the alveolar tissue, 2 main forms of this microorganism can be found: small mononuclear trophozoites (1-5 microns) and cysts multiplying by binary fission (10 microns), having a thick wall and containing from 2 to 8 cells (1-2 microns), called sporozoites. When a mature cyst ruptures, the sporozoites either continue their development cycle in the alveoli, turning into trophozoites, or go out into the environment (with droplets of mucus when coughing) and, if they acquire a new host, are also included in their development cycle.

Pneumocysts are widely distributed in humans and animals. A person becomes infected by airborne droplets.

Clinical signs of pneumocystosis are observed only in debilitated children and in immunocompromised individuals (AIDS patients, as well as patients receiving immunosuppressants). Outbreaks of pneumocystis pneumonia in hospitals where patients with the above pathology were treated were described.

Diseases develop only in individuals with primary or acquired immune disorders.

There is evidence that if AIDS patients can be saved from pneumocytosis, then their life is significantly extended.

Toxoplasmosis (Toksoplazma gondii) is the causative agent of toxoplasmosis. Class "Sporoviki".

The body of Toxoplasma has a crescent or oval shape. The anterior end of the body is pointed. The sizes of toxoplasma fluctuate from 4 to 9 microns. in length and from 2-4 microns. in width. When observed in a conventional light microscope in Toxoplasma, against the background of blue cytoplasm, a carmine-red vesicular nucleus stands out. Using an electron microscope, you can find that at the front end of the body of Toxoplasma there is a spiral structure - the so-called conoid. The thinnest fibrils (microtubules) diverge from it along the surface of the body, apparently performing the function of the motor apparatus. Peculiar strands - toxonemes - depart from the ring inside the conoid.

Toxoplasma is able to multiply in a variety of cells: macrophages, epithelial, muscle, nerve, etc. Reproduction of Toxoplasma in a cell leads to its death. As a result of the death of a group of infected cells, foci of necrosis are formed in the organs.

Immunological studies have shown that more than 500 million people are infected with Toxoplasma on Earth.

The life cycle of Toxoplasma: the stages of schizogony, gametogony and sporogony alternate in it.

Other such groups are covered with a dense shell and form cysts. Cysts are very stable and can be dormant in host organs. They are not released into the environment. The cycle of development is closed when cats eat organs of intermediate hosts with cysts.

Ways of infection with human toxoplasmosis:

When eating the meat of infested animals.

With milk and dairy products.

Through the skin and mucous membranes when caring for sick animals, when processing skins and cutting animal raw materials.

In utero through the placenta.

With medical manipulations of blood transfusion and leukocyte mass, with organ transplants, accompanied by the intake of immunosuppressive drugs.

The most dangerous is transplacental infection. In this case, the birth of children with multiple congenital malformations, primarily of the brain, is possible.

Laboratory diagnostics is based mainly on the use of serological methods: RSK, RPHA, indirect immunofluorescence reaction, latex agglutination reaction, enzyme immunoassay, etc.

The most valuable data is obtained by isolating Toxoplasma on laboratory animals infected with material from sick people.

Prevention: heat treatment of animal food, sanitary control at slaughterhouses and meat processing plants, prevention of close contact of children and pregnant women with pets.

Sarcocysts (Sarcocystys hominis, S. Suihominis, S. lindemanni) are the causative agents of sarcocystosis. The development cycle is similar to that of Toxoplasma.

The main host is man, animals are intermediate hosts. In humans, the intestines are also affected. But the degree of damage to it is very small. Doctors usually do not make a correct diagnosis, and the disease ends with a quick self-healing. Infection occurs by eating raw or undercooked meat.

Leishmania (Leischmania) - the class "Flagellates" - the causative agent of leishmaniasis.

L. donovani - the causative agent of visceral leishmaniasis;

L. tropica is the causative agent of cutaneous leishmaniasis;

L. mexicana - the causative agent of leishmaniasis in Central America;

L.brasiliensis is the causative agent of Brazilian leishmaniasis.

All species are morphologically similar and have the same cycles of development.

They exist in two forms:

flagellaless, or leishmanial (3-5 microns in diameter, with a round nucleus occupying about ¼ of the cytoplasm; there is no flagellum, a rod-shaped kinetoplast is located perpendicular to the cell surface. It lives in the cells of the human reticuloendothelial system and a number of mammals - rodents, dogs and foxes);

flagella, or promastigote (length up to 25 microns, there is a flagellum in front, at the base of which the kinetoplast is clearly visible. It lives in the digestive system of mosquitoes).

The flagellate-free form, sown on a culture medium, turns into a flagellated one. Leishmaniasis is widespread in tropical and subtropical countries on all continents where mosquitoes live. Natural reservoirs are rodents, wild and domestic animals. Human infection occurs when bitten by infested mosquitoes.

There are three main forms of leishmaniasis:

Mucocutaneous.

Visceral.

Cutaneous leishmaniasis. Runs relatively well. The lesions are in the skin.

Pathogens: in Africa and Asia - L. tropica, and in the Western Hemisphere - L. mexicana and a number of strains of L. brasiliensis.

Leishmania L. tropica and L. mexicana cause long-term non-healing ulcers on the skin at the site of mosquito bites. Ulcers heal within a few months after formation, and deep scars remain in their place. Some forms of L. brasiliensis are able to spread through the lymphatic vessels of the skin, producing numerous skin ulcers away from the bite site.

Mucocutaneous leishmaniasis.

Visceral leishmaniasis.

Laboratory diagnostics. Leishmania amastigotes are detected in smears prepared from scrapings of skin lesions, bone marrow punctate, stained with Romanovsky-Giemsa stain. In some cases, serodiagnostic reactions are used (indirect immunofluorescence, enzyme immunoassay, etc.).

Prevention: Vector control and destruction of natural reservoirs (rodents and stray dogs), as well as preventive vaccinations.

List of used literature

1. Borisov L.B. "Medical microbiology, virology, immunology".

2. Vorobyov A.A., Bykov A.S., Pashkov E.P., Rybakova A.M. "Microbiology".

3. Vorobyov A.A., Bykov A.S. "Atlas of Microbiology".

4. Pishak V.P., Bazhora Yu.I. "Medical biology".

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2.1. Systematics and nomenclature of microbes

The world of microbes can be divided into cellular and non-cellular forms. Cellular forms of microbes are represented by bacteria, fungi and protozoa. They can be called microorganisms. Non-cellular forms are represented by viruses, viroids and prions.

The new classification of cellular microbes includes the following taxonomic units: domains, kingdoms, types, classes, orders, families, genera, species. The classification of microorganisms is based on their genetic relationship, as well as morphological, physiological, antigenic and molecular biological properties.

Viruses are often considered not as organisms, but as autonomous genetic structures, so they will be considered separately.

The cellular forms of microbes are divided into three domains. Domains bacteria And Archaebacteria include microbes with a prokaryotic type of cell structure. Domain Representatives Eukarya are eukaryotes. It consists of 4 kingdoms:

Mushroom kingdoms (Fungi, Eumycota);

protozoan kingdoms (Protozoa);

kingdoms Chromista(chrome);

Microbes with unspecified taxonomic position (Microspora, microsporidia).

Differences in the organization of prokaryotic and eukaryotic cells are presented in table. 2.1.

Table 2.1. Signs of a prokaryotic and eukaryotic cell

2.2. Classification and morphology of bacteria

The term "bacteria" comes from the word bacteria, what does wand mean. Bacteria are prokaryotes. They are divided into two domains: bacteria And Archaebacteria. Bacteria in the domain archaebacteria, represent one of the oldest forms of life. They have structural features of the cell wall (they lack peptidoglycan) and ribosomal RNA. Among them, there are no pathogens of infectious diseases.

Within the domain, bacteria are subdivided into the following taxonomic categories: class, phylum, order, family, genus, species. One of the main taxonomic categories is species. A species is a collection of individuals that have a common origin and genotype, united by similar properties that distinguish them from other members of the genus. The species name corresponds to the binary nomenclature, i.e. consists of two words. For example, the causative agent of diphtheria is written as Corynebacterium diphtheriae. The first word is the name of the genus and is written with a capital letter, the second word denotes the species and is written with a lowercase letter.

When a species is mentioned again, the generic name is abbreviated to the initial letter, for example C. diphtheriae.

A set of homogeneous microorganisms isolated on a nutrient medium, characterized by similar morphological, tinctorial (relation to dyes), cultural, biochemical and antigenic properties, is called pure culture. A pure culture of microorganisms isolated from a specific source and different from other members of the species is called strain. Close to the concept of "strain" is the concept of "clone". A clone is a collection of offspring grown from a single microbial cell.

To designate some sets of microorganisms that differ in certain properties, the suffix “var” (variety) is used, therefore, microorganisms, depending on the nature of the differences, are designated as morphovars (difference in morphology), resistant products (difference in resistance, for example, to antibiotics), serovars (difference in antigens), fagovars (difference in sensitivity to bacteriophages), biovars (difference in biological properties), chemovars (difference in biochemical properties), etc.

Previously, the basis of the classification of bacteria was the structural feature of the cell wall. The subdivision of bacteria according to the structural features of the cell wall is associated with the possible variability of their coloration in one color or another according to the Gram method. According to this method, proposed in 1884 by the Danish scientist H. Gram, depending on the staining results, bacteria are divided into gram-positive, stained blue-violet, and gram-negative, stained red.

Currently, the classification is based on the degree of genetic relationship, based on the study of the structure of the ribosomal RNA (rRNA) genome (see Chapter 5), determining the percentage of guanine-cytosine pairs (GC-pairs) in the genome, constructing a genome restriction map, and studying the degree of hybridization. Phenotypic indicators are also taken into account: attitude to Gram stain, morphological, cultural and biochemical properties, antigenic structure.

Domain bacteria includes 23 types, of which the following are of medical importance.

Most gram-negative bacteria are grouped into a phylum Proteobacteria(named after the Greek god Proteus, able to take on different forms). Type Proteobacteria subdivided into 5 classes:

Class Alphaproteobacteria(birth Rickettsia, Orientia, Erlichia, Bartonella, Brucella);

Class Betaproteobacteria(birth Bordetella, Burholderia, Neisseria, Spirillum);

Class Gammaproteobacteria(members of the family enterobacteriaceae, childbirth Francisella, Legionella, Coxiella, Pseudomonas, Vibrio);

Class Deltaproteobacteria(genus Bilophila);

Class Epsilonproteobacteria(birth Campylobacter, Helicobacter). Gram-negative bacteria are also included in the following types:

type Chlamydiae(birth Chlamydia, Chlamydophila) type Spirochaetes(birth Spirocheta, Borrelia, Treponema, Leptospira); type Bacteroides(birth Bacteroides, Prevotella, Porphyromonas).

Gram-positive bacteria come in the following types:

Type Firmicutes includes class Clostridium(birth Clostridium, Peptococcus), Class Bacilli (Listeria, Staphylococcus, Lactobacillus, Streptococcus) and class Mollicutes(birth Mycoplasma, Ureaplasma), which are bacteria that do not have a cell wall;

type Actinobacteria(birth Actinomyces, Micrococcus, Corynebacterium, Mycobacterium, Gardnerella, Bifidobacterium, Propionibacterium, Mobiluncus).

2.2.1. Morphological forms of bacteria

There are several basic forms of bacteria: coccoid, rod-shaped, convoluted and branching (Fig. 2.1).

Spherical shapes, or cocci- spherical bacteria 0.5-1 microns in size, which are divided by mutual arrangement into micrococci, diplococci, streptococci, tetracocci, sarcins and staphylococci.

Micrococci (from the Greek. micros- small) - separately located cells.

Diplococci (from the Greek. diploos- double), or paired cocci, arranged in pairs (pneumococcus, gonococcus, meningococcus), since the cells do not diverge after division. Pneumococcus (the causative agent of pneumonia) has a lanceolate shape on opposite sides, and gonococcus (the causative agent of gonorrhea) and meningococcus (causative agent)

Rice. 2.1. Shapes of bacteria

cause of epidemic meningitis) are shaped like coffee beans with their concave surfaces facing each other.

Streptococci (from the Greek. streptos- chain) - cells of a rounded or elongated shape that make up a chain due to cell division in the same plane and maintaining the connection between them at the place of division.

Sarcins (from lat. Sarcina- bundle, bale) are arranged in the form of packages of 8 cocci or more, since they are formed during cell division in three mutually perpendicular planes.

Staphylococci (from the Greek. staphyle- bunch of grapes) - cocci arranged in the form of a bunch of grapes as a result of division in different planes.

rod-shaped bacteria differ in size, shape of the ends of the cell and the relative position of the cells. Cell length 1-10 µm, thickness 0.5-2 µm. Sticks can be right

(E. coli, etc.) and irregular club-shaped (corynebacteria, etc.) forms. Rickettsiae are among the smallest rod-shaped bacteria.

The ends of the sticks can be, as it were, cut off (anthrax bacillus), rounded (E. coli), pointed (fusobacteria) or in the form of a thickening. In the latter case, the stick looks like a mace (Corynebacterium diphtheria).

The slightly curved rods are called vibrios (Vibrio cholerae). Most rod-shaped bacteria are arranged randomly, because after division, the cells diverge. If after division the cells remain connected by common fragments of the cell wall and do not diverge, then they are located at an angle to each other (corynebacterium diphtheria) or form a chain (anthrax bacillus).

Convoluted shapes- spiral-shaped bacteria, which are of two types: spirilla and spirochetes. Spirilla have the appearance of corkscrew-shaped convoluted cells with large curls. Pathogenic spirillae include the causative agent of sodoku (rat bite disease), as well as campylobacter and helicobacteria, which have curves resembling the wings of a flying gull. Spirochetes are thin, long, convoluted bacteria that differ from spirilla in smaller curls and in the nature of movement. Their structure is described below.

branching - rod-shaped bacteria, which may have a Y-shaped branching, found in bifidobacteria, can also be presented as filamentous branched cells that can intertwine to form a mycelium, which is observed in actinomycetes.

2.2.2. Structure of a bacterial cell

The structure of bacteria is well studied using electron microscopy of whole cells and their ultrathin sections, as well as other methods. A bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the shell is protoplasm, consisting of cytoplasm with inclusions and a hereditary apparatus - an analogue of the nucleus, called the nucleoid (Fig. 2.2). There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria under adverse conditions are able to form spores.

Rice. 2.2. Structure of a bacterial cell: 1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - mesosomes; 5 - nucleoid; 6 - plasmid; 7 - ribosomes; 8 - inclusions; 9 - flagellum; 10 - drank (villi)

cell wall- a strong, elastic structure that gives the bacteria a certain shape and, together with the underlying cytoplasmic membrane, restrains high osmotic pressure in the bacterial cell. It is involved in the process of cell division and transport of metabolites, has receptors for bacteriophages, bacteriocins and various substances. The thickest cell wall in gram-positive bacteria (Fig. 2.3). So, if the thickness of the cell wall of gram-negative bacteria is about 15-20 nm, then in gram-positive bacteria it can reach 50 nm or more.

The cell wall of bacteria is made up of peptidoglycan. Peptidoglycan is a polymer. It is represented by parallel polysaccharide glycan chains, consisting of repeating residues of N-acetylglucosamine and N-acetylmuramic acid connected by a glycosidic bond. This bond is broken by lysozyme, which is acetylmuramidase.

A tetrapeptide is attached to N-acetylmuramic acid by covalent bonds. The tetrapeptide consists of L-alanine, which is linked to N-acetylmuramic acid; D-glutamine, which in gram-positive bacteria is connected to L-lysine, and in gram-positive bacteria

Rice. 2.3. Scheme of the architectonics of the bacterial cell wall

bacteria - with diaminopimelic acid (DAP), which is a precursor of lysine in the process of bacterial biosynthesis of amino acids and is a unique compound found only in bacteria; The 4th amino acid is D-alanine (Fig. 2.4).

The cell wall of gram-positive bacteria contains a small amount of polysaccharides, lipids and proteins. The main component of the cell wall of these bacteria is a multilayer peptidoglycan (murein, mucopeptide), which makes up 40-90% of the mass of the cell wall. Tetrapeptides of different layers of peptidoglycan in gram-positive bacteria are connected to each other by polypeptide chains of 5 glycine (pentaglycine) residues, which gives the peptidoglycan a rigid geometric structure (Fig. 2.4, b). Covalently bound to the peptidoglycan of the cell wall of Gram-positive bacteria teichoic acids(from Greek. tekhos- wall), the molecules of which are chains of 8-50 residues of glycerol and ribitol connected by phosphate bridges. The shape and strength of the bacteria is given by the rigid fibrous structure of the multilayer, with cross-linked peptide cross-links of peptidoglycan.

Rice. 2.4. Structure of peptidoglycan: a - Gram-negative bacteria; b - gram-positive bacteria

The ability of gram-positive bacteria to retain gentian violet in combination with iodine (blue-violet color of bacteria) during Gram staining is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, the subsequent treatment of a smear of bacteria with alcohol causes a narrowing of the pores in peptidoglycan and thereby retains the dye in the cell wall.

Gram-negative bacteria after exposure to alcohol lose the dye, which is due to a smaller amount of peptidoglycan (5-10% of the mass of the cell wall); they are discolored with alcohol, and when treated with fuchsin or safranin, they become red. This is due to the structural features of the cell wall. Peptidoglycan in the cell wall of gram-negative bacteria is represented by 1-2 layers. The tetrapeptides of the layers are interconnected by a direct peptide bond between the amino group of DAP of one tetrapeptide and the carboxyl group of D-alanine of the tetrapeptide of another layer (Fig. 2.4, a). Outside of peptidoglycan is a layer lipoprotein, bound to peptidoglycan via DAP. It is followed by outer membrane cell wall.

outer membrane is a mosaic structure represented by lipopolysaccharides (LPS), phospholipids and proteins. Its inner layer is represented by phospholipids, and LPS is located in the outer layer (Fig. 2.5). Thus, the outer mem-

Rice. 2.5. Structure of lipopolysaccharide

the brane is asymmetric. The LPS of the outer membrane consists of three fragments:

Lipid A - a conservative structure, almost the same in gram-negative bacteria. Lipid A consists of phosphorylated glucosamine disaccharide units to which long chains of fatty acids are attached (see Figure 2.5);

The core, or rod, of the cow part (from lat. core- core), relatively conservative oligosaccharide structure;

A highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences.

LPS is anchored in the outer membrane by lipid A, which determines the toxicity of LPS and is therefore identified with endotoxin. The destruction of bacteria by antibiotics leads to the release of large amounts of endotoxin, which can cause endotoxic shock in the patient. From lipid A, the core, or the core part of the LPS, departs. The most constant part of the core of LPS is ketodeoxyoctonic acid. O-specific polysaccharide chain extending from the core part of the LPS molecule,

consisting of repeating oligosaccharide units, determines the serogroup, serovar (a type of bacteria detected using immune serum) of a certain strain of bacteria. Thus, the concept of LPS is associated with ideas about the O-antigen, according to which bacteria can be differentiated. Genetic changes can lead to defects, shortening of the LPS of bacteria and, as a result, the appearance of rough colonies of R-forms that lose their O-antigen specificity.

Not all Gram-negative bacteria have a complete O-specific polysaccharide chain consisting of repeating oligosaccharide units. In particular, bacteria of the genus Neisseria have a short glycolipid called lipooligosaccharide (LOS). It is comparable to the R-form, which has lost O-antigenic specificity, observed in mutant rough strains. E. coli. The structure of the VOC resembles that of the human cytoplasmic membrane glycosphingolipid, so the VOC mimics the microbe, allowing it to evade the host's immune response.

The proteins of the matrix of the outer membrane permeate it in such a way that the protein molecules, called porins, they border hydrophilic pores through which water and small hydrophilic molecules with a relative mass of up to 700 D pass.

Between the outer and cytoplasmic membranes is periplasmic space, or periplasm containing enzymes (proteases, lipases, phosphatases, nucleases, β-lactamases), as well as components of transport systems.

In case of violation of the synthesis of the bacterial cell wall under the influence of lysozyme, penicillin, protective factors of the body and other compounds, cells with an altered (often spherical) shape are formed: protoplasts- bacteria completely devoid of a cell wall; spheroplasts Bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i. acquire a full-fledged cell wall and restore its original shape.

Bacteria of the spheroid or protoplast type that have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to multiply are called L-shaped(from the name of the D. Lister Institute, where they first

you have been studied). L-forms can also arise as a result of mutations. They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable) when the factor that led to changes in the bacteria is removed, can reverse, returning to the original bacterial cell. L-forms can form many pathogens of infectious diseases.

cytoplasmic membrane under electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers 2.5 nm thick each are separated by a light one - intermediate). In structure, it is similar to the plasmolemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins, as if penetrating through the membrane structure. Some of them are permeases involved in the transport of substances. Unlike eukaryotic cells, there are no sterols in the cytoplasmic membrane of a bacterial cell (with the exception of mycoplasmas).

The cytoplasmic membrane is a dynamic structure with mobile components, therefore it is presented as a mobile fluid structure. It surrounds the outer part of the cytoplasm of bacteria and is involved in the regulation of osmotic pressure, transport of substances and energy metabolism of the cell (due to the enzymes of the electron transport chain, adenosine triphosphatase - ATPase, etc.). With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complexly twisted membrane structures, called mesosomes. Less complex twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes has not been fully elucidated. It is even suggested that they are an artifact that occurs after the preparation (fixation) of the preparation for electron microscopy. Nevertheless, it is believed that derivatives of the cytoplasmic membrane participate in cell division, providing energy for the synthesis of the cell wall, take part in the secretion of substances, spore formation, i.e. in processes with high energy consumption. The cytoplasm occupies the bulk of the bacterial

a nal cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes responsible for the synthesis (translation) of proteins.

Ribosomes bacteria have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to the 80S ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics bind to bacterial ribosomes and inhibit bacterial protein synthesis without affecting protein synthesis in eukaryotic cells. Bacterial ribosomes can dissociate into two subunits: 50S and 30S. rRNA - conservative elements of bacteria ("molecular clock" of evolution). 16S rRNA is part of the small subunit of ribosomes, and 23S rRNA is part of the large subunit of ribosomes. The study of 16S rRNA is the basis of gene systematics, making it possible to assess the degree of relatedness of organisms.

In the cytoplasm there are various inclusions in the form of glycogen granules, polysaccharides, β-hydroxybutyric acid and polyphosphates (volutin). They accumulate with an excess of nutrients in the environment and serve as reserve substances for nutrition and energy needs.

Volyutin has an affinity for basic dyes and is easily detected using special staining methods (for example, according to Neisser) in the form of metachromatic granules. Toluidine blue or methylene blue stains volutin red-violet, and the bacterial cytoplasm blue. The characteristic arrangement of volutin granules is revealed in diphtheria bacillus in the form of intensely stained poles of the cell. Metachromatic staining of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1–1 µm in size.

Nucleoid is the equivalent of the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, tightly packed like a ball. The bacterial nucleoid, unlike eukaryotes, does not have a nuclear envelope, nucleolus, and basic proteins (histones). Most bacteria contain one chromosome, represented by a DNA molecule closed in a ring. But some bacteria have two ring-shaped chromosomes. (V. cholerae) and linear chromosomes (see section 5.1.1). The nucleoid is detected under a light microscope after staining with specific DNA

methods: according to Felgen or according to Romanovsky-Giemsa. On electron diffraction patterns of ultrathin sections of bacteria, the nucleoid has the form of light zones with fibrillar, thread-like structures of DNA associated with certain areas with the cytoplasmic membrane or mesosome involved in chromosome replication.

In addition to the nucleoid, the bacterial cell contains extrachromosomal factors of heredity - plasmids (see section 5.1.2), which are covalently closed DNA rings.

Capsule, microcapsule, mucus.Capsule - a mucous structure more than 0.2 microns thick, firmly associated with the bacterial cell wall and having clearly defined outer boundaries. The capsule is distinguishable in smears-imprints from pathological material. In pure cultures of bacteria, the capsule is formed less frequently. It is detected by special methods of smear staining according to Burri-Gins, which create a negative contrast of the capsule substances: the ink creates a dark background around the capsule. The capsule consists of polysaccharides (exopolysaccharides), sometimes polypeptides, for example, in the anthrax bacillus, it consists of polymers of D-glutamic acid. The capsule is hydrophilic, contains a large amount of water. It prevents phagocytosis of bacteria. The capsule is antigenic: antibodies to the capsule cause its increase (capsule swelling reaction).

Many bacteria form microcapsule- mucous formation with a thickness of less than 0.2 microns, detected only with electron microscopy.

To be distinguished from a capsule slime - mucoid exopolysaccharides that do not have clear external boundaries. Slime is soluble in water.

Mucoid exopolysaccharides are characteristic of mucoid strains of Pseudomonas aeruginosa, often found in the sputum of patients with cystic fibrosis. Bacterial exopolysaccharides are involved in adhesion (sticking to substrates); they are also called glycocalyx.

The capsule and mucus protect bacteria from damage and drying out, since, being hydrophilic, they bind water well and prevent the action of protective factors of the macroorganism and bacteriophages.

Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments that take on

originating from the cytoplasmic membrane, are longer than the cell itself. The flagella are 12–20 nm thick and 3–15 µm long. They consist of three parts: a spiral thread, a hook and a basal body containing a rod with special disks (one pair of disks in gram-positive and two pairs in gram-negative bacteria). The discs of the flagella are attached to the cytoplasmic membrane and cell wall. This creates the effect of an electric motor with a rod - a rotor that rotates the flagellum. The difference of proton potentials on the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The speed of rotation of the flagellum can reach 100 rpm. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.

Flagella are made up of a protein called flagellin. (flagellum- flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are coiled.

The number of flagella in bacteria of different species varies from one (monotrich) in Vibrio cholerae to ten or hundreds extending along the perimeter of the bacterium (peritrich), in Escherichia coli, Proteus, etc. Lofotrichs have a bundle of flagella at one end of the cell. Amphitrichous have one flagellum or a bundle of flagella at opposite ends of the cell.

Flagella are detected using electron microscopy of preparations sprayed with heavy metals, or in a light microscope after processing by special methods based on etching and adsorption of various substances, leading to an increase in the thickness of the flagella (for example, after silvering).

Villi, or pili (fimbriae)- filamentous formations, thinner and shorter (3-10 nm * 0.3-10 microns) than flagella. Pili extend from the cell surface and are composed of the pilin protein. Several types of saws are known. Pili of a general type are responsible for attachment to the substrate, nutrition and water-salt metabolism. They are numerous - several hundred per cell. Sex pili (1-3 per cell) create contact between cells, transferring genetic information between them by conjugation (see Chapter 5). Of particular interest are type IV pili, in which the ends are hydrophobic, as a result of which they twist, these pili are also called curls. Located-

they are located at the poles of the cell. These pili are found in pathogenic bacteria. They have antigenic properties, make contact between the bacterium and the host cell, and participate in the formation of a biofilm (see Chapter 3). Many pili are receptors for bacteriophages.

Disputes - a peculiar form of resting bacteria with a gram-positive type of cell wall structure. spore-forming bacteria of the genus bacillus, in which the size of the spore does not exceed the diameter of the cell, are called bacilli. Spore-forming bacteria in which the size of the spore exceeds the diameter of the cell, which is why they take the form of a spindle, are called clostridia, such as bacteria of the genus Clostridium(from lat. Clostridium- spindle). The spores are acid-resistant, therefore they are stained red according to the Aujeszky method or according to the Ziehl-Nelsen method, and the vegetative cell is blue.

Sporulation, the shape and location of spores in a cell (vegetative) are a species property of bacteria, which makes it possible to distinguish them from each other. The shape of the spores is oval and spherical, the location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in pathogens of botulism, gas gangrene) and central (in anthrax bacilli).

The process of sporulation (sporulation) goes through a series of stages, during which part of the cytoplasm and the chromosome of a bacterial vegetative cell are separated, surrounded by a growing cytoplasmic membrane, and a prospore is formed.

The prospore protoplast contains a nucleoid, a protein-synthesizing system, and an energy-producing system based on glycolysis. Cytochromes are absent even in aerobes. Does not contain ATP, energy for germination is stored in the form of 3-glycerol phosphate.

The prospore is surrounded by two cytoplasmic membranes. The layer that surrounds the inner membrane of the spore is called spore wall, it consists of peptidoglycan and is the main source of the cell wall during spore germination.

Between the outer membrane and the spore wall, a thick layer is formed, consisting of peptidoglycan, which has many crosslinks, - cortex.

Outside of the outer cytoplasmic membrane is located spore shell, consisting of keratin-like proteins,

containing multiple intramolecular disulfide bonds. This shell provides resistance to chemical agents. Spores of some bacteria have an additional cover - exosporium lipoprotein nature. Thus, a multilayer poorly permeable shell is formed.

Sporulation is accompanied by intensive consumption by the prospore, and then by the emerging spore shell of dipicolinic acid and calcium ions. The spore acquires heat resistance, which is associated with the presence of calcium dipicolinate in it.

The spore can persist for a long time due to the presence of a multi-layered shell, calcium dipicolinate, low water content and sluggish metabolic processes. In the soil, for example, anthrax and tetanus pathogens can persist for decades.

Under favorable conditions, spores germinate through three successive stages: activation, initiation, growth. In this case, one bacterium is formed from one spore. Activation is the readiness for germination. At a temperature of 60-80 °C, the spore is activated for germination. Germination initiation takes several minutes. The growth stage is characterized by rapid growth, accompanied by the destruction of the shell and the release of the seedling.

2.2.3. Features of the structure of spirochetes, rickettsiae, chlamydia, actinomycetes and mycoplasmas

Spirochetes- thin long convoluted bacteria. They consist of an outer membranous cell wall that surrounds the cytoplasmic cylinder. On top of the outer membrane is a transparent sheath of glycosaminoglycan nature. Under the outer membrane cell wall, fibrils are located, twisting around the cytoplasmic cylinder, giving the bacteria a helical shape. Fibrils are attached to the ends of the cell and directed towards each other. The number and arrangement of fibrils varies in different species. Fibrils are involved in the movement of spirochetes, giving the cells rotational, flexion and translational motion. In this case, spirochetes form loops, curls, bends, which are called secondary curls. Spirochetes do not perceive dyes well. Usually they are stained according to Romanovsky-Giemsa or silvered. Live

the form of a spirochete is examined using phase-contrast or dark-field microscopy.

Spirochetes are represented by three genera pathogenic to humans: Treponema, Borrelia, Leptospira.

Treponema(genus Treponema) have the appearance of thin corkscrew-twisted threads with 8-12 uniform small curls. There are 3-4 fibrils (flagella) around the treponema protoplast. The cytoplasm contains cytoplasmic filaments. Pathogenic representatives are T. pallidum- causative agent of syphilis T.pertenue- the causative agent of a tropical disease - yaws. There are also saprophytes - inhabitants of the human oral cavity, silt of reservoirs.

Borrelia(genus Borrelia, unlike treponemas, they are longer, have 3-8 large curls and 7-20 fibrils. These include the causative agent of relapsing fever (V. recurrentis) and the causative agents of Lyme disease (B. burgdorferi) and other diseases.

Leptospira(genus Leptospira) have curls that are shallow and frequent in the form of a twisted rope. The ends of these spirochetes are curved like hooks with thickenings at the ends. Forming secondary curls, they take the form of the letters S or C; have two axial fibrils. Pathogenic representative L. interrogans causes leptospirosis when ingested with water or food, leading to hemorrhages and jaundice.

Rickettsia have a metabolism independent of the host cell, however, they may receive macroergic compounds from the host cell for their reproduction. In smears and tissues, they are stained according to Romanovsky-Giemsa, according to Machiavello-Zdrodovsky (rickettsia are red, and infected cells are blue).

Rickettsia causes epidemic typhus in humans. (R. prowazekii), tick-borne rickettsiosis (R. sibirica), Rocky Mountain spotted fever (R. rickettsii) and other rickettsiosis.

The structure of their cell wall resembles that of gram-negative bacteria, although there are differences. It does not contain typical peptidoglycan: N-acetylmuramic acid is completely absent in its composition. The cell wall consists of a double outer membrane, which includes lipopolysaccharide and proteins. Despite the absence of peptidoglycan, the chlamydia cell wall is rigid. The cytoplasm of the cell is limited by the inner cytoplasmic membrane.

The main method for detecting chlamydia is the Romanovsky-Giemsa stain. The color of the stain depends on the stage of the life cycle: elementary bodies turn purple against the background of the blue cytoplasm of the cell, reticular bodies turn blue.

In humans, chlamydia causes damage to the eyes (trachoma, conjunctivitis), urogenital tract, lungs, etc.

actinomycetes- branching, filamentous or rod-shaped gram-positive bacteria. Its name (from the Greek. actis- Ray, mykes- fungus) they received in connection with the formation of drusen in the affected tissues - granules of tightly interwoven threads in the form

rays extending from the center and ending in flask-shaped thickenings. Actinomycetes, like fungi, form mycelium - filamentous intertwining cells (hyphae). They form substrate mycelium, which is formed as a result of cells growing into the nutrient medium, and air, growing on the surface of the medium. Actinomycetes can divide by fragmenting the mycelium into cells similar to rod-shaped and coccoid bacteria. On aerial hyphae of actinomycetes, spores are formed that serve for reproduction. Actinomycete spores are usually not heat resistant.

A common phylogenetic branch with actinomycetes is formed by the so-called nocardio-like (nocardioform) actinomycetes - a collective group of irregularly shaped rod-shaped bacteria. Their individual representatives form branching forms. These include bacteria of the genera Corynebacterium, Mycobacterium, Nocardia and others. Nocardioid actinomycetes are distinguished by the presence in the cell wall of the sugars of arabinose, galactose, as well as mycolic acids and large amounts of fatty acids. Mycolic acids and cell wall lipids determine the acid resistance of bacteria, in particular Mycobacterium tuberculosis and leprosy (when stained according to Ziehl-Nelsen, they are red, and non-acid-resistant bacteria and tissue elements, sputum are blue).

Pathogenic actinomycetes cause actinomycosis, nocardia - nocardiosis, mycobacteria - tuberculosis and leprosy, corynebacteria - diphtheria. Saprophytic forms of actinomycetes and nocardia-like actinomycetes are widespread in the soil, many of them are producers of antibiotics.

Mycoplasmas- small bacteria (0.15-1 µm) surrounded only by a cytoplasmic membrane containing sterols. They belong to the class Mollicutes. Due to the lack of a cell wall, mycoplasmas are osmotically sensitive. They have a variety of shapes: coccoid, filiform, flask-shaped. These forms are visible on phase-contrast microscopy of pure cultures of mycoplasmas. On a dense nutrient medium, mycoplasmas form colonies resembling fried eggs: a central opaque part immersed in the medium and a translucent periphery in the form of a circle.

Mycoplasmas cause SARS in humans (Mycoplasma pneumoniae) and lesions of the urinary tract

(M. hominis and etc.). Mycoplasmas cause diseases not only in animals but also in plants. Non-pathogenic representatives are quite widespread.

2.3. The structure and classification of mushrooms

Mushrooms belong to the domain eukarya, kingdom Fungi (Mycota, Mycetes). Fungi and protozoa have recently been divided into independent kingdoms: the kingdom Eumycota(true mushrooms), kingdom Chromista and kingdom Protozoa. Some microorganisms previously thought to be fungi or protozoa have been moved to a new kingdom Chromista(chromes). Mushrooms are multicellular or unicellular non-photosynthetic (chlorophyll-free) eukaryotic microorganisms with a thick cell wall. They have a nucleus with a nuclear membrane, a cytoplasm with organelles, a cytoplasmic membrane, and a multilayered rigid cell wall consisting of several types of polysaccharides (mannans, glucans, cellulose, chitin), as well as protein, lipids, etc. Some fungi form a capsule. The cytoplasmic membrane contains glycoproteins, phospholipids and ergosterols (in contrast to cholesterol, the main sterol of mammalian tissues). Most fungi are obligate or facultative aerobes.

Fungi are widely distributed in nature, especially in the soil. Some mushrooms contribute to the production of bread, cheese, dairy products and alcohol. Other fungi produce antimicrobial antibiotics (eg penicillin) and immunosuppressive drugs (eg cyclosporine). Fungi are used by geneticists and molecular biologists to model various processes. Phytopathogenic fungi cause significant damage to agriculture, causing fungal diseases of cereal plants and grain. Infections caused by fungi are called mycoses. There are hyphae and yeast fungi.

Hyphal (mold) fungi, or hyphomycetes, consist of thin threads 2-50 microns thick, called hyphae, which are woven into a mycelium or mycelium (mold). The body of the fungus is called the thallus. Distinguish demacia (pigmented - brown or black) and hyaline (non-pigmented) hyphomycetes. Hyphae growing into the nutrient substrate are responsible for the nutrition of the fungus and are called vegetative hyphae. Hyphae, ra-

growing above the surface of the substrate are called aerial or reproductive hyphae (responsible for reproduction). Colonies due to aerial mycelium have a fluffy appearance.

There are lower and higher fungi: the hyphae of higher fungi are separated by partitions, or septa with holes. The hyphae of lower fungi do not have partitions, representing multinucleated cells called coenocytic (from the Greek. koenos- single, general).

Yeast fungi (yeast) are mainly represented by individual oval cells with a diameter of 3-15 microns, and their colonies, unlike hyphal fungi, have a compact appearance. According to the type of sexual reproduction, they are distributed among higher fungi - ascomycete and basidiomycete. During asexual reproduction, yeasts form buds or divide. They can form pseudohyphae and false mycelium (pseudomycelium) in the form of chains of elongated cells - "wieners". Mushrooms that are similar to yeast but do not reproduce sexually are called yeast-like. They reproduce only asexually - by budding or division. The concepts of "yeast-like fungi" are often identified with the concept of "yeast".

Many fungi have dimorphism - the ability to hyphal (mycelial) or yeast-like growth, depending on the cultivation conditions. In an infected organism, they grow as yeast-like cells (yeast phase), and form hyphae and mycelium on nutrient media. Dimorphism is associated with a temperature factor: at room temperature, mycelium is formed, and at 37 ° C (at human body temperature), yeast-like cells are formed.

Fungi reproduce either sexually or asexually. Sexual reproduction of fungi occurs with the formation of gametes, sexual spores and other sexual forms. Sexual forms are called teleomorphs.

Asexual reproduction of fungi occurs with the formation of the corresponding forms, called anamorphs. Such reproduction occurs by budding, fragmentation of hyphae and asexual spores. Endogenous spores (sporangiospores) mature inside a rounded structure - sporangia. Exogenous spores (conidia) are formed at the tips of fruiting hyphae, the so-called conidiophores.

There are various conidia. Arthroconidia (arthrospores), or talloconidia, are formed with uniform septation and dissection of hyphae, and blastoconidia are formed as a result of budding. Small unicellular conidia are called microconidia, large multicellular conidia are called macroconidia. The asexual forms of fungi also include chlamydoconidia, or chlamydospores (thick-walled large resting cells or a complex of small cells).

There are perfect and imperfect mushrooms. Perfect mushrooms have a sexual mode of reproduction; they include zygomycetes (Zygomycota), ascomycetes (Ascomycota) and basidiomycetes (Basidiomycota). Imperfect fungi have only asexual reproduction; these include a formal conditional type / group of fungi - deuteromycetes (Deiteromycota).

Zygomycetes belong to the lower fungi (non-septate mycelium). They include members of the genus Mucor, Rhizopus, Rhizomucor, Absidia, Basidiobolus, Conidiobolus. Distributed in soil and air. They can cause zygomycosis (mucormycosis) of the lungs, brain and other human organs.

During asexual reproduction of zygomycetes on a fruiting hypha (sporangiophore), a sporangium is formed - a spherical thickening with a shell containing numerous sporangiospores (Fig. 2.6, 2.7). Sexual reproduction in zygomycetes occurs with the help of zygospores.

Ascomycetes (marsupials) have septate mycelium (except for unicellular yeasts). They got their name from the main fruiting organ - the bag, or ascus, containing 4 or 8 haploid sexual spores (ascospores).

Ascomycetes include individual representatives (teleomorphs) of the genera Aspergillus And Penicillium. Most mushroom genera Aspergillus, Penicillium are anamorphs, i.e. breed only harmlessly

Rice. 2.6. Mushrooms of the genus Mucor(Fig. A.S. Bykov)

Rice. 2.7. Mushrooms of the genus Rhizopus. Development of sporangia, sporangiospores and rhizoids

in a lym way with the help of asexual spores - conidia (Fig. 2.8, 2.9) and should be classified according to this feature as imperfect fungi. In fungi of the genus Aspergillus at the ends of fruit-bearing hyphae, conidiophores, there are thickenings - sterigmas, phialides, on which chains of conidia are formed ("lech mold").

In fungi of the genus Penicillium(racus) the fruiting hypha resembles a brush, since thickenings are formed from it (on the conidiophore), branching into smaller structures - sterigmas, phialides, on which there are chains of conidia. Some types of aspergillus can cause aspergillosis and aflatoxicosis, penicillium can cause penicilliosis.

Representatives of ascomycetes are teleomorphs of the genera Trichophyton, Microsporum, Histoplasma, Blastomyces, as well as trembling

Rice. 2.8. Mushrooms of the genus Penicillium. Chains of conidia extend from the phialides

Rice. 2.9. Mushrooms of the genus Aspergillus fumigatus. Chains of conidia extend from the phialides

Basidiomycetes include cap mushrooms. They have a septate mycelium and form sexual spores - basidiospores by lacing off from the basidium - the end cell of the mycelium, homologous to the ascus. Some yeasts, such as teleomorphs, are basidiomycetes. Cryptococcus neoformans.

Deuteromycetes are imperfect fungi (Fungi imperfecti, anamorphic fungi, conidial fungi). This is a conditional, formal taxon of fungi, uniting fungi that do not have sexual reproduction. Recently, instead of the term "deuteromycetes", the term "mitosporous fungi" has been proposed - fungi that reproduce by asexual spores, i.e. by mitosis. When establishing the fact of sexual reproduction of imperfect fungi, they are transferred to one of the known types - Ascomycota or Basidiomycota, giving the name of the teleomorphic form. Deuteromycetes have septate mycelium and reproduce only by asexual formation of conidia. Deuteromycetes include imperfect yeasts (yeast-like fungi), for example, some fungi of the genus Candida affecting the skin, mucous membranes and internal organs (candidiasis). They are oval in shape, 2-5 microns in diameter, divide by budding, form pseudohyphae (pseudomycelium) in the form of chains of elongated cells, sometimes form hyphae. For candida albicans the formation of chlamydospores is characteristic (Fig. 2.10). Deuteromycetes also include other fungi that do not have a sexual mode of reproduction, related to genera Epidermophyton, Coccidioides, Paracoccidioides, Sporothrix, Aspergillus, Phialophora, Fonsecaea, Exophiala, Cladophialophora, Bipolaris, Exerohilum, Wangiella, Alrernaria and etc.

Rice. 2.10. Mushrooms of the genus candida albicans(Fig. A.S. Bykov)

2.4. Structure and classification of protozoa

The simplest belong to the domain eukarya, animal kingdom (Animalia) sub-kingdom Protozoa. Recently it has been proposed to single out protozoa to the rank of kingdom Protozoa.

The protozoan cell is surrounded by a membrane (pellicle) - an analogue of the cytoplasmic membrane of animal cells. It has a nucleus with a nuclear envelope and nucleolus, a cytoplasm containing the endoplasmic reticulum, mitochondria, lysosomes and ribosomes. The sizes of protozoa range from 2 to 100 microns. When stained according to Romanovsky-Giemsa, the nucleus of the protozoa is red, and the cytoplasm is blue. Protozoa move with the help of flagella, cilia or pseudopodia, some of them have digestive and contractile (excretory) vacuoles. They can feed as a result of phagocytosis or the formation of special structures. By type of nutrition, they are divided into heterotrophs and autotrophs. Many protozoa (dysentery amoeba, Giardia, Trichomonas, Leishmania, Balantidia) can grow on nutrient media containing native proteins and amino acids. Cell cultures, chicken embryos and laboratory animals are also used for their cultivation.

The simplest reproduce asexually - by double or multiple (schizogony) division, and some also sexually (sporogony). Some protozoa reproduce extracellularly (Giardia), while others reproduce intracellularly (Plasmodium, Toxoplasma, Leishmania). The life cycle of protozoa is characterized by stages - the formation of the trophozoite stage and the cyst stage. Cysts are dormant stages resistant to changes in temperature and humidity. Cysts are acid resistant Sarcocystis, Cryptosporidium And Isospora.

Previously, the protozoa that cause disease in humans were represented by 4 types 1 ( Sarcomastigophora, Apicomplexa, Ciliophora, Microspora). These types have recently been reclassified to a larger number, new realms have appeared - Protozoa And Chromista(Table 2.2). To a new kingdom Chromista(chromovics) included some protozoa and fungi (blastocysts, oomycetes and Rhinosporidium seeberi). Kingdom Protozoa includes amoeba, flagellates, sporozoans and ciliates. They are divided into different types, among which there are amoeba, flagellates, sporozoans and ciliates.

Table 2.2. Kingdom representatives Protozoa And Chromista, of medical importance

1 type Sarcomastigophora consisted of subtypes Sarcodina And Mastigophora. Subtype Sarcodina(sarcode) included the dysenteric amoeba, and the subtype Mastigophora(flagellates) - trypanosomes, leishmania, giardia and Trichomonas. Type Apicomplexa included class Sporozoa(sporozoa), which included malaria plasmodia, toxoplasma, cryptosporidium, etc. Type Ciliophora includes balantidia, and the type Microspora- microsporidia.

The end of the table. 2.2

Amoebas are the causative agent of human amoebiasis - amoebic dysentery (Entamoeba histolytica), free-living and non-pathogenic amoeba (intestinal amoeba, etc.). Amoebas reproduce binary asexually. Their life cycle consists of the trophozoite stage (growing, mobile cell, unstable) and the cyst stage. Trophozoites move with the help of pseudopodia, which capture and immerse nutrients into the cytoplasm. From

trophozoite, a cyst is formed that is resistant to external factors. Once in the intestine, it turns into a trophozoite.

Flagellates are characterized by the presence of flagella: Leishmania has one flagellum, Trichomonas has 4 free flagella and one flagellum connected to a short undulating membrane. They are:

Flagellates of blood and tissues (leishmania - causative agents of leishmaniasis; trypanosomes - causative agents of sleeping sickness and Chagas disease);

Intestinal flagellates (giardia - the causative agent of giardiasis);

Flagellates of the genitourinary tract (Trichomonas vaginalis - the causative agent of trichomoniasis).

Ciliated are represented by balantidia, which affect the human large intestine (balantidiasis dysentery). Balantidia have a trophozoite and a cyst stage. The trophozoite is mobile, has numerous cilia, thinner and shorter than the flagella.

2.5. The structure and classification of viruses

Viruses are the smallest microbes belonging to the kingdom Virae(from lat. virus- I). They do not have a cellular structure and are

The structure of viruses, due to their small size, is studied using electron microscopy of both virions and their ultrathin sections. The size of viruses (virions) is determined directly using electron microscopy or indirectly by ultrafiltration through filters with a known pore diameter, by ultracentrifugation. The size of viruses ranges from 15 to 400 nm (1 nm is equal to 1/1000 microns): small viruses, the size of which is similar to the size of ribosomes, include parvoviruses and poliovirus, and the largest ones are variola virus (350 nm). Viruses differ in the form of virions, which have the form of rods (tobacco mosaic virus), bullets (rabies virus), spheres (polio viruses, HIV), filaments (filoviruses), sperm (many bacteriophages).

Viruses amaze the imagination with their variety of structure and properties. Unlike cellular genomes, which contain uniform double-stranded DNA, viral genomes are extremely diverse. There are DNA- and RNA-containing viruses that are haploid, i.e. have one set of genes. Only retroviruses have a diploid genome. The genome of viruses contains from 6 to 200 genes and is represented by various types of nucleic acids: double-stranded, single-stranded, linear, circular, fragmented.

Among single-stranded RNA-containing viruses, genomic plus-strand RNA and minus-strand RNA (RNA polarity) are distinguished. Plus-thread (positive thread) of RNA of these viruses, in addition to the genomic (hereditary) function, performs the function of information, or matrix RNA (mRNA, or mRNA); it is a template for protein synthesis on the ribosomes of the infected cell. Plus-strand RNA is infectious: when introduced into sensitive cells, it can cause an infectious pro-

cess. The negative thread (negative thread) of RNA-containing viruses performs only a hereditary function; for protein synthesis, a complementary strand is synthesized on the negative strand of RNA. Some viruses have an ambipolar RNA genome. (Ambience from the Greek ambi- on both sides, double complementarity), i.e. contains plus and minus RNA segments.

A distinction is made between simple viruses (eg hepatitis A virus) and complex viruses (eg influenza, herpes, coronaviruses).

Simple, or non-enveloped, viruses have only a nucleic acid associated with a protein structure called a capsid (from lat. capsa- case). The proteins associated with the nucleic acid are known as nucleoproteins, and the association of the viral capsid proteins of the virus with the viral nucleic acid is called the nucleocapsid. Some simple viruses can form crystals (eg foot-and-mouth disease virus).

The capsid includes repeating morphological subunits - capsomeres, composed of several polypeptides. The nucleic acid of the virion binds to the capsid to form the nucleocapsid. The capsid protects the nucleic acid from degradation. In simple viruses, the capsid is involved in attachment (adsorption) to the host cell. Simple viruses leave the cell as a result of its destruction (lysis).

Complex, or enveloped, viruses (Fig. 2.11), in addition to the capsid, have a membrane double lipoprotein shell (synonym: supercapsid, or peplos), which is acquired by budding the virion through the cell membrane, for example, through the plasma membrane, nuclear membrane or endoplasmic reticulum membrane. On the envelope of the virus are glycoprotein spikes,

or spines, ash meters. The destruction of the shell with ether and other solvents inactivates complex viruses. Under the shell of some viruses is a matrix protein (M-protein).

Virions have a helical, icosahedral (cubic) or complex type of capsid (nucleocapsid) symmetry. The helical type of symmetry is due to the helical structure of the nucleocapsid (for example, in influenza viruses, coronaviruses): capsomeres are stacked in a spiral along with the nucleic acid. The icosahedral type of symmetry is due to the formation of an isometric hollow body from a capsid containing a viral nucleic acid (for example, in the herpes virus).

The capsid and the shell (supercapsid) protect virions from environmental influences, determine the selective interaction (adsorption) of their receptor proteins with a certain

Rice. 2.11. The structure of enveloped viruses with icosahedral (a) and helical (b) capsid

cells, as well as antigenic and immunogenic properties of virions.

The internal structures of viruses are called the core. In adenoviruses, the core consists of histone-like proteins associated with DNA; in reoviruses, it consists of proteins of the internal capsid.

Nobel Prize winner D. Baltimore proposed a Baltimore classification system based on the mechanism of mRNA synthesis. This classification places viruses in 7 groups (Table 2.3). International Committee on Taxonomy of Viruses (ICTV) adopted a universal classification system that uses taxonomic categories such as family (the name ends with viridae), subfamily (name ends with virinae), genus (name ends with virus). The type of virus has not received a binomial name, as in bacteria. Viruses are classified according to the type of nucleic acid (DNA or RNA), its structure and the number of strands. They have double-stranded or single-stranded nucleic acids; positive (+), negative (-) nucleic acid polarity or mixed nucleic acid polarity, ambipolar (+, -); linear or circular nucleic acid; fragmented or non-fragmented nucleic acid. The size and morphology of virions, the number of capsomeres and the type of symmetry of the nucleocapsid, the presence of a shell (supercapsid), sensitivity to ether and deoxycholate, the place of reproduction in the cell, antigenic properties, etc. are also taken into account.

Table 2.3. Major viruses of medical importance

Continuation of the table. 2.3

The end of the table. 2.3

Viruses infect animals, bacteria, fungi and plants. Being the main causative agents of human infectious diseases, viruses also participate in the processes of carcinogenesis, can be transmitted in various ways, including through the placenta (rubella virus, cytomegalovirus, etc.), affecting the human fetus. They can also lead to post-infectious complications - the development of myocarditis, pancreatitis, immunodeficiency, etc.

Non-cellular life forms, in addition to viruses, include prions and viroids. Viroids are small molecules of circular, supercoiled RNA that do not contain protein and cause diseases in plants. Pathological prions are infectious protein particles that cause special conformational diseases as a result of a change in the structure of the normal cellular prion protein ( PrP c), which is found in the body of animals and humans. PrP with performs regulatory functions. It is encoded by the normal prion gene (PrP gene) located on the short arm of the 20th human chromosome. Prion diseases proceed according to the type of transmissible spongiform encephalopathy (Crutzfeldt-Jakob disease, kuru, etc.). In this case, the prion protein acquires a different, infectious form, designated as PrP sc(sc from scrapie- scrapie - prion infection of sheep and goats). This infectious prion protein is fibril-like and differs from the normal prion protein in its tertiary or quaternary structure.

Tasks for self-training (self-control)

A. Name the microbes that are prokaryotes:

2. Viruses.

3. Bacteria.

4. Prions.

B. List the characteristics of a prokaryotic cell:

1. Ribosomes 70S.

2. The presence of peptidoglycan in the cell wall.

3. The presence of mitochondria.

4. Diploid set of genes.

IN. List the components of peptidoglycan:

1. Teichoic acids.

2. N-acetylglucosamine.

3. Lipopolysarid.

4. Tetrapeptide.

G. Note the structural features of the cell wall of Gram-negative bacteria:

1. Mesodiaminopimelic acid.

2. Teichoic acids.

4. Porin proteins.

D. Name the functions of spores in bacteria:

1. Save the view.

2. Heat resistance.

3. Settlement of the substrate.

4. Reproduction.

1. Rickettsia.

2. Actinomycetes.

3. Spirochetes.

4. Chlamydia.

AND. Name the features of actinomycetes:

1. They have heat-labile spores.

2. Gram-positive bacteria.

3. There is no cell wall.

4. Have a twisted shape.

Z. Name the features of spirochetes:

1. Gram-negative bacteria.

2. They have a motor fibrillar apparatus.

3. They have a twisted shape.

AND. Name the protozoa that have an apical complex that allows them to penetrate inside the cell:

1. Malarial Plasmodium.

3. Toxoplasma.

4. Cryptosporidium.

TO. Name the distinguishing feature of complexly organized viruses:

1. Two types of nucleic acid.

2. The presence of a lipid membrane.

3. Double capsid.

4. The presence of non-structural proteins. L. Mark the higher mushrooms:

1. Mucor.

2. Candida.

3. Penicillium.

4. Aspergillus.