13 morphology of mycoplasmas species pathogenic for humans. Topic: Morphology of actinomycetes, mycoplasmas, rickettsia, chlamydia and fungi. Structure of a bacterial cell

Mycoplasmas are characterized by extremely pronounced polymorphism, primarily due to the absence of a solid cell wall inherent in bacteria, as well as a complex development cycle. smallest structural elements capable of reproduction in artificial nutrient media, commonly referred to as the minimum reproductive units. The shape and size of the minimum reproductive units, as well as cellular elements of different stages of development, are significantly affected by the cultivation conditions, the physicochemical properties of nutrient media, the characteristics of the strain and the number of passages on the media, the technique of preparing, fixing and staining preparations, and other factors.
Due to the fact that mycoplasmas do not have a cell wall, their membrane and cytoplasm are easily damaged by chemical reagents used for fixing and staining preparations. Mycoplasma cells in the early stages of development are especially sensitive to environmental factors.
In smears from the affected organs and from cultures grown in the environment, mycoplasmas are represented by round, oval and annular formations. Sometimes there are coccobacillary and bacteria-like forms. Separate types mycoplasmas (M. mycoides var. mycoides, M. mycoides var. capri, M. agalacliae) form filamentous mycelial forms in organs and nutrient media.
Electron microscopic studies and by filtering grown cultures through membrane filters with a known hole diameter showed that in the same culture there are formations of various shapes and sizes that are capable of reproduction (Fig. 1). When researching various kinds mycoplasmas isolated from animal and human organs, as well as environmental objects, it was found that the value elementary particles ranges from 125 to 600 im. In the determinant of Berge, the size of mycoplasma cells is estimated at 125-200 nm. According to E. Freundt, the size of the minimum reproductive units of mycoplasmas ranges between 250-300 nm. Other authors determined their size in the range of 200-500-700 nm, and G. Wildfur, using the ultrafiltration method. - 100-150 nm. It should be noted that the size of mycoplasma cells depends not only on the species and strain, but also on other factors affecting the cell.
Thus, the size of the minimum reproductive units in cultures of mycoplasmas varies considerably.

Mycoplasmas. Taxonomy. Characteristic. Microbiological diagnostics. Treatment.

Anthroponotic bacterial infections in humans affecting the respiratory or genitourinary tract.

Mycoplasmas belong to the class Mollicutes, which includes 3 orders: Acholeplasmatales, Mycoplasmatales, Anaeroplasmatales.

Morphology: The absence of a rigid cell wall, cell polymorphism, plasticity, osmotic sensitivity, resistance to various agents that inhibit cell wall synthesis, including penicillin and its derivatives. Gram "-", better stained according to Romanovsky-Giemsa; Distinguish between movable and immovable types. The cell membrane is in a liquid-crystalline state; includes proteins immersed in two lipid layers, the main component of which is cholesterol.

cultural properties. Chemoorganotrophs, the main source of energy is glucose or arginine. Grow at 30C. Most species are facultative anaerobes; extremely demanding on nutrient media and cultivation conditions. Nutrient media (beef heart extract, yeast extract, peptone, DNA, glucose, arginine).

Cultivated on liquid, semi-liquid and dense nutrient media.

Biochemical activity: Low. There are 2 groups of mycoplasmas: 1. decomposing glucose, maltose, mannose, fructose, starch and glycogen with the formation of acid; 2. oxidizing glutamate and lactate, but not fermenting carbohydrates. All species do not hydrolyze urea.

Antigenic structure: Complex, has specific differences; the main AGs are represented by phospho- and glycolipids, polysaccharides and proteins; The most immunogenic are superficial AGs, which include carbohydrates as part of complex glycolipid, lipoglycan, and glycoprotein complexes.

Pathogenic factors: adhesins, toxins, aggression enzymes and metabolic products. Adhesins are part of surface antigens and cause adhesion to host cells. Suggested presence of neurotoxin in some strains M. pneumoniae, since respiratory tract infections often accompany lesions nervous system. Endotoxins have been isolated from many pathogenic mycoplasmas. Some species have hemolysins. Among the aggression enzymes, the main pathogenicity factors are phospholipase A and aminopeptidases, which hydrolyze cell membrane phospholipids. Proteases causing degranulation of cells, including mast cells, cleavage of AT molecules and essential amino acids.

Epidemiology: M. pneumoniae colonizes the mucous membrane of the respiratory tract; M. hominis, M. genitalium u U. urealyticum- "urogenital mycoplasmas" - live in the urogenital tract.

The source of infection is a sick person. The transmission mechanism is aerogenic, the main route of transmission is airborne.

Pathogenesis: They penetrate the body, migrate through the mucous membranes, attach to the epithelium through glycoprotein receptors. Microbes do not show a pronounced cytopathogenic effect, but cause disturbances in cell properties with the development of local inflammatory reactions.

Clinic: Respiratory mycoplasmosis - in the form of an infection of the upper respiratory tract, bronchitis, pneumonia. Extra-respiratory manifestations: hemolytic anemia, neurological disorders, complications from the cardiovascular system.

Immunity: cases of re-infection are typical for respiratory and urogenital mycoplasmosis.

Microbiological diagnostics: swabs from the nasopharynx, sputum, bronchial washings. In urogenital infections, urine, scrapings from the urethra, vagina are examined.

For laboratory diagnosis of mycoplasmal infections, cultural, serological and molecular genetic methods are used.

In serodiagnosis, smears-imprints of tissues, scrapings from the urethra, vagina, in which it is possible to detect mycoplasma AG in direct and indirect RIF, serve as the material for research. Mycoplasmas and ureaplasmas are detected as green granules.

AG mycoplasmas can also be detected in the blood serum of patients. For this, ELISA is used.

For serodiagnosis of respiratory mycoplasmosis, specific antibodies are determined in paired patient sera. In urogenital mycoplasmosis, in some cases, serodiagnosis is carried out, AT is most often determined in RPHA and ELISA.

Treatment. Antibiotics. Etiotropic chemotherapy.

Prevention. Nonspecific.

The causative agent of chlamydia. Taxonomy. Feature. Microbiological diagnostics. Treatment.

Taxonomy: order Chlamydiales, family Chlamydaceae, genus Chlamydia. The genus is represented by the species C.trachomatis, C.psittaci, C.pneumoniae.

Diseases caused by chlamydia are called chlamydia. Diseases caused C. trachomatis u C. pneumoniae,- anthroponoses. Ornithosis, the causative agent of which is C. psittaci- zooanthroponic infection.

Morphology of chlamydia: small, gram "-" bacteria, spherical shape. Do not form spores, no flagella and capsules. Cell wall: 2-layer membrane. They have glycolipids. Gram is red. The main staining method is according to Romanovsky-Giemsa.

2 forms of existence: elementary bodies (inactive infectious particles, outside the cell); reticular bodies (inside cells, vegetative form).

Cultivation: Can only be propagated in living cells. In the yolk sac of developing chicken embryos, sensitive animals and in cell culture

Enzymatic activity: small. They ferment pyruvic acid and synthesize lipids. Not capable of synthesizing high-energy compounds.

Antigenic structure: Antigens of three types: genus-specific thermostable lipopolysaccharide (in the cell wall). Identified with the help of RSK; species-specific antigen of a protein nature (in the outer membrane). Detect using RIF; variant-specific antigen of a protein nature.

pathogenicity factors. The proteins of the outer membrane of chlamydia are associated with their adhesive properties. These adhesins are found only in elementary bodies. Chlamydia produce endotoxin. Heat shock protein found in some chlamydiae , capable of inducing autoimmune reactions.

resistance. High various factors external environment. Resistant to low temperatures, drying. Sensitive to heat.

C. trachomatis- the causative agent of diseases of the genitourinary system, eyes and respiratory tract of a person.

Trachoma is a chronic infectious disease characterized by damage to the conjunctiva and cornea of the eyes. Anthroponosis. Transmitted by contact-household way.

Pathogenesis: affects the mucous membrane of the eyes. It penetrates the epithelium of the conjunctiva and cornea, where it multiplies, destroying cells. Follicular keratoconjunctivitis develops.

Diagnostics: examination of scrapings from the conjunctiva. In the affected cells, when stained according to Romanovsky-Giemsa, cytoplasmic inclusions of purple color are found, located near the nucleus - Provachek's body. RIF and ELISA are also used to detect a specific chlamydial antigen in affected cells. Sometimes they resort to the cultivation of chlamydia trachoma on chicken embryos or cell culture.

Treatment: antibiotics (tetracycline) and immunostimulants (interferon).

Prevention: Nonspecific.

Urogenital chlamydia is a sexually transmitted disease. This is an acute / chronic infectious disease, which is characterized by a predominant lesion of the genitourinary tract.

Human infection occurs through the mucous membranes of the genital tract. The main mechanism of infection is contact, the mode of transmission is sexual.

Immunity: cellular, with the serum of infected - specific antibodies. After the transferred disease - it is not formed.

Diagnostics: In diseases of the eyes, a bacterioscopic method is used - intracellular inclusions are detected in scrapings from the epithelium of the conjunctiva. RIF is used to detect chlamydia antigen in affected cells. In case of damage to the genitourinary tract, a biological method can be applied, based on infection with the test material (scrapings of the epithelium from the urethra, vagina) of cell culture.

Statement RIF, ELISA allow you to detect chlamydia antigens in the test material. Serological method - to detect IgM against C. trachomatis in the diagnosis of neonatal pneumonia.

Treatment. antibiotics (azithromycin from the macrolide group), immunomodulators, eubiotics.

Prevention. Only non-specific (treatment of patients), personal hygiene.

Venereal lymphogranuloma is a sexually transmitted disease characterized by lesions of the genital organs and regional lymph nodes. The mechanism of infection is contact, the route of transmission is sexual.

Immunity: persistent, cellular and humoral immunity.

Diagnostics: The material for the study is pus, biopsy from the affected lymph nodes, blood serum. Bacterioscopic method, biological (cultivation in the yolk sac of a chicken embryo), serological (RCC with paired sera is positive) and allergological (intradermal test with chlamydia allergen) methods.

Treatment.Antibiotics - macrolides and tetracyclines.

Prevention: Nonspecific.

C. pneumoniae - causative agent of respiratory chlamydia, causes acute and chronic bronchitis and pneumonia. Anthroponosis. Infection is by airborne droplets. They enter the lungs through the upper respiratory tract. Cause inflammation.

Diagnostics: setting RSK for the detection of specific antibodies (serological method). In primary infection, IgM detection is taken into account. RIF is also used to detect chlamydial antigen and PCR.

Treatment: Carried out with the help of antibiotics (tetracyclines and macrolides).

Prevention: Non-specific.

C. psittaci - the causative agent of ornithosis - an acute infectious disease, which is characterized by damage to the lungs, nervous system and parenchymal organs (liver, spleen) and intoxication.

Zooanthroponosis. Sources of infection - birds. The mechanism of infection is aerogenic, the route of transmission is airborne. The causative agent is through the mucus. shells breathe. pathways, into the epithelium of the bronchi, alveoli, multiplies, inflammation.

Diagnostics: The material for the study is blood, sputum of the patient, blood serum for serological testing.

A biological method is used - the cultivation of chlamydia in the yolk sac of a chicken embryo, in cell culture. Serological method. Apply RSK, RPHA, ELISA, using paired blood serum of the patient. Intradermal allergy test with ornithine.

Treatment: antibiotics (tetracyclines, macrolides).

The causative agent of typhus. Taxonomy. Feature. Brill-Zinsser disease. Microbiological diagnostics. Specific prevention and treatment.

epidemic typhus - acute anthroponosis with a transmissible mechanism of distribution by body lice. Clinically characterized by fever, severe course due to damage to blood capillaries with impaired blood supply to vital organs (brain, heart, kidneys), the appearance of a rash.

Epidemiology and mechanism of infection. Infection is realized either by rubbing the feces of infected lice through scratching the skin, or by inhaling a dusty aerosol from dried rickettsia-infected feces.

Clinic, diagnosis, treatment. The incubation period is 10 days. The onset of the disease is acute, clinical manifestations are due to a generalized lesion of the system of endothelial cells of blood vessels, which leads to disruption of the cascade of thrombo-antithrombotic formation. The morphological basis of the disease is generalized vasculitis with the formation of a rash on the skin. The disease proceeds with high fever, symptoms of damage to the cardiovascular and nervous systems. Immunity- short, cellular-humoral.

Diagnostics: carried out according to clinical and epidemiological data, supported by a laboratory test for specific antibodies (RSK, RNGA, ELISA, etc.).

Treatment: Rapid etiotropic treatment with a single dose of doxycycline, in its absence - with tetracycline drugs.

Prevention. Isolation of lice patients, disinfection with preparations containing permethrin. For specific prophylaxis, a live vaccine from strain E has been developed, which is used in combination with a soluble antigen of Rickettsia Provachek (a live combined typhoid vaccine from a strain), as well as an inactivated vaccine from a soluble antigen.

Brill's disease – relapse after a previous epidemic typhus.

Pathogen- R. prowazekii.

Clinically proceeds as epidemic typhus of mild to moderate severity.

Pathomorphology infectious process is the same as in the epidemic form. The difference lies in the epidemiology (there is no carrier, there is no seasonal manifestation, the source and implementation of the method of infection) and the pathogenesis of the initial stage of the disease. It arises due to the activation of latently "dormant" rickettsiae.

Microbiological diagnostics. It is hampered by the uncertainty of symptoms in the first week of the disease (before the appearance of a rash) and its similarity with symptoms in infections, more often typhoid. The diagnosis is established on the basis of clinical and epidemiological data, taking into account the patient's history and is supported by a serological study with a specific antigen. In the absence of a vector in the focus, treatment can be carried out without isolation of the patient, depending on his condition. The prognosis is good even in the absence of antibiotic treatment.

Prevention. Preventive measures are the same as in the epidemic form. Specific prophylaxis is not possible.

Mycoplasmas are tiny particles. They are the smallest self-replicating prokaryotes. The morphology and size of mycoplasmas vary depending on the age of the culture, conditions and culture media. Mycoplasmas are polymorphic. Mycoplasma cells are limited only by a three-layer plasma membrane (intraplasmic membranes were not found in mycoplasmas). In 1935, filterable, cell wallless forms were isolated from the bacteria Streptobacillus moniliformis, which remarkably resembled mycoplasmas. Recently, they have been called L-forms of bacteria. The state of the L-form is due to the influence of adverse environmental factors (for example, the use of antibiotics that act on the cell wall). In their absence, the L-form is reversible. In mycoplasmas, unlike other bacteria, the state of the L-form, i.e. the absence of a cell wall is their usual state.

The absence of a cell wall in mycoplasmas determines their plasticity, which allows these microorganisms to penetrate through the pores of filters with a diameter of 0.22 - 0.45 microns. Due to the filterability of mycoplasmas, they have long been confused with viruses. The spherical shape of the cells is characteristic of most types of mycoplasmas. At the same time, cells of the same mycoplasma can be spherical (or somewhat elongated) 0.3–0.8 µm in diameter, but can form long (up to 100 µm), sometimes branching strands, which, passing through the phase of coccoid structures, disintegrate into a number of spherical cells, which is shown in Figure 2. Coccoid structures sometimes form a ring.

Mycoplasmas do not form so-called resting forms or spores. Like other non-spore-forming bacteria, mycoplasmas become unculturable under unfavorable conditions, and also form "minimal bodies" that are not capable of reproduction, since they probably do not contain DNA.

Figure 2

a) - morphological transformations under optimal cultivation conditions in vitro
b) - morphological forms under suboptimal conditions, at the stationary phase of culture growth

Some types of mycoplasmas have sliding mobility. The cells of such mycoplasmas have special structures and cytoskeleton-like formations. Thus, M. gallisepticum cells are pear-shaped, M. pneumoniae are also pear-shaped, but more elongated, and M. mycoides are more often cord-shaped.

The cells of most bacteria can be covered with a shell - a polymeric substance that has many properties and functions. This shell, or capsule, is different from the two-layer membrane and is located above it. In bacteria, the term "capsule" is used to refer to the high molecular weight polymers that "attach" to the surface of the bacteria. Although the peptidoglycan cell wall, which is characteristic of most prokaryotes, is absent in representatives of the Mollicutes class, capsules or capsule-like structures have been described for some types of mycoplasmas. They are possessed by Mycoplasma mycoides, M. gallisepticum, M. hyopneumoniae, M. meleagridis, M. dispar, M. pneumoniae, M. pulmonis, M. synoviae, M. hominis. Among ureaplasmas, only some strains of Ureaplasma urealitycum are able to form capsules.

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Topic 3: Morphology and ultrastructure of individual groups of microorganisms: rickettsiae, chlamydia, mycoplasmas, actinomycetes, spirochetes, fungi, protozoa

Target occupation: to know morphology and ultrastructure of rickettsia, chlamydia, mycoplasmas, actinomycetes, fungi, protozoa; be able to describe the main properties of representatives of the microcosm, use the microscopic method in the diagnosis of infectious diseases (prepare smears from the material under study, stain them using various staining methods, microscope with oil immersion, describe morphological and tinctorial properties)

Homework:

I. Questions for self-study:

I. List the features of the structure and reproduction of actinomycetes. List the features of the structure, reproduction of rickettsia. List the features of the structure and reproduction of chlamydia. List the features of the structure, detection, chemical composition of mycoplasmas. List the features of the structure, movement, color of spirochetes. List the structural features, reproduction of fungi, types of mycelium, spores. List the main representatives of pathogenic protozoa, their morphological features, staining methods.

II. actinomycetes

Actinomycetes are microorganisms that occupy an intermediate position between bacteria and fungi. long time actinomycetes were considered fungi, but the study of morphology and biological properties made it possible to attribute them to bacteria of the family Actinomycetaceae department Firmicutes. The similarity with fungi is determined by the ability to form substrate and aerial mycelium on a nutrient medium, at the ends of which spores are formed; actinomycete spores are a way of reproduction. However, unlike fungi, the cell wall of actinomycetes does not contain chitin or cellulose; they are not capable of photosynthesis, and the mycelium they form is rather primitive. They are also resistant to antifungal drugs. What unites actinomycetes with bacteria is the absence of a clearly defined nucleus, the presence of a cell wall, as well as sensitivity to bacteriophages and antibiotics.

Actinomycetes are 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 - colonies consisting of granules of tightly interwoven threads in the form of rays extending from the center and ending in flask-shaped thickenings. Non-acid resistant. facultative anaerobes. Actinomycetes can divide by fragmenting the mycelium into cells similar to rod-shaped and flask-shaped bacteria. Spores of actinomycetes are usually heat-resistant.

Most actinomycetes live on the surface of the mucous membranes in mammals; some species are soil saprophytes. In humans, actinomycetes colonize the mucous membranes of the oral cavity and gastrointestinal tract. The ability to cause specific lesions is not very pronounced and they are considered as conditional pathogens. Bacteria cause actinomycosis - chronic purulent granulomatous lesions of various organs.

The vast majority of cases of actinomycosis in humans are caused by A.israelii, in rare cases of A.naeslundii, A.odontolyticus, A.bovis, A.viscosus.

/. Rickettsia

actively multiply by binary fission in the cytoplasm, and some - in the nucleus of infected cells, using the energy systems of the host cell, since Spiro is not able to synthesize the NAD coenzyme and other metabolites. The resting form has an increased resistance with a thickened cell wall and compacted cytoplasm.

They live in the body of arthropods (lice, fleas, ticks), which are their hosts or carriers. The shape and size of rickettsia can change (cells irregular shape, filiform, coccoid, bacillary) depending on growth conditions. In smears and tissues, they are stained according to Romanovsky-Giemsa, according to Zdrodovsky or according to Machiavello (rickettsia are red, and infected cells are blue).

Rickettsia pathogenic for humans cause rickettsiosis; among them there are groups of typhus (R.prowazekii, R.typhi) and spotted fevers (R.ricketsii, R.conorii), Q fever (C.burnetii) and etc.

2. Chlamydia

Chlamydia are obligate intracellular coccoid gram-negative fibril (sometimes gram-variable) bacteria. They reproduce only in living cells. Outside the cells, chlamydia are spherical (0.3 μm), metabolically inactive, and are called elementary bodies. The cell wall of elementary bodies contains the main protein of the outer membrane and a protein containing a large amount of cysteine. Elementary bodies enter the epithelial cell by endocytosis with the formation of an intracellular vacuole. Inside the cells, they increase and turn into dividing reticular bodies, forming clusters in vacuoles (inclusions). From the reticular bodies, elementary bodies are formed, which exit the cells by exocytosis or cell lysis. The elementary bodies that have left the cell enter a new cycle, infecting other cells.

Chlamydia are studied in a living state using phase-contrast microscopy and stained according to the Romanovsky-Giemsa method (elementary bodies are stained pink, reticular bodies are blue-blue), as well as in the immunofluorescence reaction (RIF), etc.

In humans, chlamydia is caused by: C. trachomatis(the causative agent of trachoma, urogenital infections), C.psittaci(ornithosis), C. rpeitoniae(various forms of respiratory infections).

3. Mycoplasmas

damaged but not killed. Mycoplasmas are studied in native preparations using phase-contrast microscopy, RIF, etc.

Topic 3. MORPHOLOGY OF MAIN GROUPS OF BACTERIA. MORPHOLOGY OF MUSHROOMS AND PROTOISTS. STRUCTURE OF A MICROBIAL CELL. METHODS FOR DETECTING INCLUSIONS AND ORGANOSES

The shape is divided into several groups: round (cocci), rod-shaped (actually bacteria, bacilli), curved and convoluted (vibrios, spirilla and spirochetes).
Cocci have a diameter of 1-2 microns. The shape of cocci is diverse: more often round or oval, but can be lanceolate (pneumococci) and bean-shaped (gono- and meningococci).
Cocci, like other bacteria, reproduce by simple division. According to the mutual arrangement of cells after division, they distinguish: micrococci - cells diverge and are located separately; staphylococci (for example, Staphylococcus aureus) - cells divide randomly and are arranged in groups resembling grapes; diplococci - cells do not diverge and are arranged in two, for example, pneumo-, gono- and meningococci (Fig. 2). If cocci divide in the same plane and, without diverging after division, form a chain, then they are called streptococci, for example S. lactis, S. haemolyticus. If cell division occurs in two mutually perpendicular planes and cocci are arranged in four cells, then they are called tetracocci (bacteria of the genus Gaffkya). When the division of cocci occurs in three mutually perpendicular planes, packets or sardines are formed (for example, Planosarcina ureae). Globular bacteria stain positively for Gram, with the exception of gonococci and meningococci, which are gram-negative.
Rod-shaped bacteria are very diverse in size, mutual arrangement and shape.

Rice. 2. The main groups of bacteria.
a - coccal forms: 1 - micrococci; 2 - diplococci (gonococci, meningococci); 3 - diplococci (pneumococci); 4 - tetracocci; b - staphylococci; 5 - streptococci; 7 - sardines; b - bacterial non-spore-forming forms: 1 - Escherichia coli; 2 - diphtheria bacillus; c - spore-forming bacteria (bacilli and clostridia): 1 - anthrax bacilli; 2-oily-acidic clostridia; 3 - tetanus sticks (plectridium); g - curved and convoluted forms: 1 - cholera vibrios; 2 - spirilla; 3 - treponema; 4 - Borrelia; b - leptospira; e - actinomycetes: 1st direct spore-bearing; 2 - with indirect spore bearers; 3 - unicellular mycelium.
Eni can be small (0.5-1X0.3 microns), medium-sized (2X0.5 microns) and large - up to 5-8 microns in length; in shape - cylindrical with rounded, chopped off, pointed, thickened and other shapes. Rods that do not form spores are called bacteria proper, those that form spores are called bacilli. Bacteria generally do not stain for Gram (gram-negative), with the exception of lactobacilli, which stain gram-positive. They can form capsules and show mobility due to the presence of flagella.
Bacteria and bacilli can be located randomly, one by one, but often form more or less long chains (streptobacteria and streptobacilli). If the cells are grouped in twos, then they speak of diplobacteria and diplobacilli.
Rod-shaped bacteria are widely represented in nature. Among them are many saprophytes causing putrefactive processes(bacilli and some bacteria). Many non-spore-forming rods are pathogenic or opportunistic for mammals (for example, bacteria of the genus Shigella, Salmonella, Klebsiella, Pseudomonas, etc.). Anaerobic bacilli can also cause disease, such as Clostridium perfringens - the causative agent of gas gangrene, C. tetani - the causative agent of tetanus.
Slightly curved rods are called vibrios. Some of them have one terminal flagellum (for example, Vibrio cholerae), sizes from 1 to 3 microns, do not form spores, are gram-negative. Many saprophytic and pathogenic forms of vibrios live mainly in water.
The convoluted forms include spirilla and spirochetes. Spirilla are Gram-negative bacteria different amount curls, rather large (length 5-10 microns, some species reach 30 microns). The vast majority are saprophytes, found in water, soil, and the composition of normal human microflora.
Spirochetes have a number of features. The protoplasm is delimited by the cytoplasmic membrane, the weak cell membrane contains a thin peptidoglycan layer, between the cell wall and the cytoplasmic membrane there are bundles of fibrils that twist around the body of the spirochete, they give the cell a helical shape and determine its movement. Microorganisms are very diverse in shape, size and other characteristics. Body sizes vary widely depending on the species (length 10-50 microns, diameter 0.1-0.6 microns). Pathogenic species have a length of 3-20 microns. Many of them are saprophytes and are more common in water. Pathogenic spirochetes belong to the genera Treponema, Borrelia, Leptospira. A specific color for the detection of spirochetes is the Romanovsky-Giemsa method. In addition, they can be detected in preparations stained by Burri (negative method) or in "hanging" and "crushed" drops. Vital preparations are examined using a dark-field or phase-contrast device, while the features of movement and morphology of spirochetes are clearly visible.
Actinomycetes are gram-positive bacteria, a distinctive feature of some of them is the presence of mycelium, consisting of branching unicellular filaments (hyphae), 0.3-0.8 microns wide, up to 600 microns long. There are lower and higher forms. The higher forms of actinomycetes stably form mycelium, which can grow into the nutrient medium (substrate mycelium) and develop above it in the form of a loose layer (aerial mycelium).

Morphological features of rickettsia, chlamydia, mycoplasmas, their systematics, classification. Morphology of the vegetative and dormant stages

Rickettsia are named after the American scientist Ricketts, who described the causative agent of rickettsiosis. They have all the structures inherent in prokaryotes: a cell wall (it contains muramic acid), a nucleoid, and ribosomes. Spores, flagella, capsules do not have.

Gram-negative, stained according to Romanovsky-Giemsa in lilac, according to Zdrodovsky (analogous to the Ziehl-Nielsen method) - in red. Rickettsia are polymorphic, i.e., they have different morphological forms: coccoid (0.5 microns); rod-shaped (1.5 microns); bacillary (2-4 microns); filiform (10-40 microns).

Rickettsia reproduce by simple division, and filamentous forms by crushing. Cause typhus and other rickettsiosis.

Chlamydia (chlamydis - raincoat). Chlamydia are separated into a separate order Chlamydiales, which includes 4 families. The leading human pathogenic representatives of chlamydia are concentrated in the families Chlamydiaceae and Parachlamydiaceae, which include, respectively, the genera Chlamydia and Chlamydophila. The main, most important representatives of these genera in human pathology are C. psittaci, C. pneumoniae, C. trachomatis.

Elementary bodies are 0.3 μm in size, contain a nucleoid, and there is a layer in the cell wall - an analog of peptidoglycan of Gram-negative bacteria. ETs enter the cell during phagocytosis. From the surface membranes of the host cell around the ET, a vacuole is formed and the ETs turn into large reticular bodies (diameter 0.5–1 µm). Inside the formed vacuole, the RT divides many times. Ultimately, after 8-12 cycles of division, the vacuole is filled with these particles and turns into a microcolony (inclusion). At the last generation, ETs of a new generation are formed from RT. Then the membrane that surrounds the microcolony is destroyed, and chlamydia enter the cytoplasm, and then outside the cell. Diagnostic value is the detection of cytoplasmic inclusions of RT or small EBs, which differ from the cell nucleus and cytoplasm in color and internal structure. Chlamydia causes trachoma, ornithosis, venereal lymphogranulomatosis, blenorrhea with inclusions.

CHAPTER 2 MORPHOLOGY AND CLASSIFICATION OF MICROBES

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);

Kingdoms of Protozoa (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, according to the relative position, are divided 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 the preservation of the connection between them at the place of division.

Sarcins (from lat. Sarcina- a bunch, a 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 a 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. The 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.

To N-acetylmuramic acid covalent bonds attached tetrapeptide. 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 that is present 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 has a conservative structure, almost the same in gram-negative bacteria. Lipid A is composed of phosphorylated glucosamine disaccharide units to which long chains are attached. fatty acids(see fig. 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 bacterial LPS, 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 are involved 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

ali cells 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. rRNAs are conservative elements of bacteria (the "molecular clock" of evolution). 16S rRNA is part of the small ribosome subunit, and 23S rRNA is part of the large ribosome subunit. 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 act 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 a 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 different types 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 between them genetic information 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 the 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. The 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 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 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- mushroom) 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 nocardioid (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 cause nocardiosis, mycobacteria cause tuberculosis and leprosy, and corynebacteria cause 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 envelope, cytoplasm with organelles, cyto plasma membrane and a multilayer 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 use genetics and molecular biologists for simulation 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 fission. The concepts of "yeast-like fungi" are often identified with the concept of "yeast".

Many fungi are dimorphic - 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 the 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 - sporangium. 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

ly 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 membrane and a 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 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 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, motile 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 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 envelope (supercapsid) protect the virions from exposure environment, cause selective interaction (adsorption) with 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, immunodeficiencies, 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:

B. List the characteristics of a prokaryotic cell:

2. The presence of peptidoglycan in the cell wall.

3. The presence of mitochondria.

4. Diploid set of genes.

IN. Check constituent components peptidoglycan:

1. Teichoic acids.

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

1. Mesodiaminopimelic acid.

2. Teichoic acids.

D. Name the functions of spores in bacteria:

1. Save the view.

3. Settlement of the substrate.

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.

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. Note the higher mushrooms.

This review is devoted to the current state of the problem of mycoplasmal infection in children. Information is presented on the taxonomic position of various types of mycoplasmas, their morphological structure, pathogenicity, epidemiology, the most common and rare forms of the disease, methods of diagnosis and treatment in children. Keywords: mycoplasma infection, etiology, diagnosis, epidemiology, treatment

Mycoplasmosis in children:

solved and unsolved problems

Russian State Medical University, Moscow

The present review deals with the state of the art of the problem of mycoplasmic infection in children, presenting the data on taxonomic position of various species of mycoplasmata, their morphological structure, pathogenicity , epidemiology, most common and uncommon forms of the disease, as well as diagnostic and therapeutic methods in children. Key words: mycoplasmic infection, aetiology, diagnosis, epidemiology, treatment

Active study of diseases of mycoplasmal etiology began in the middle of the 20th century. Over the past period of time, a number of works have been published concerning certain issues of mycoplasmology. The fundamental works published in the 1970-80s in our country reflected many of the problems associated with mycoplasma infection in both adults and children. In recent years, diseases caused by mycoplasmas have attracted the attention of various specialists - pediatricians, pulmonologists, urologists, surgeons, endocrinologists, and cardiologists. This circumstance can be explained. on the one hand, the wide circulation of the pathogen in the external environment, on the other hand, the introduction of modern research methods, thanks to which our understanding of various forms of the disease has been significantly expanded. microbiology of mycoplasmas, cytopathogenicity of the pathogen.

Historical reference

The first information about mycoplasmas appeared in 1896, when a pathogenic member of the family was isolated - the causative agent of bovine pleuropneumonia - Pleuropneumoniaeorganism. The generally accepted name for this group of pathogens is mycoplasma, which has stuck with them to this day, suggested by E. Novak in 1929.

In the 1930s and 40s, a group of diseases of a non-bacterial nature was identified, which were called "atypical pneumonias". Numerous attempts to isolate the pathogen, as well as experiments on infecting various animal species, did not give positive results. Therefore, it was quite rightly believed that this pathogen has a viral nature. Only in 1942, M.D. Eaton succeeded in isolating an agent 180-250 nm in size from the patient's sputum, which was passaged during inoculation on chicken embryos. In 1963, this agent was recognized as a mycoplasma (Mycoplasmapneumoniae). According to its cultural properties, it belongs to Gram-negative bacteria.

taxonomic position

According to the existing modern classification Mycoplasmas belong to the microorganism class Mollicutes, which is subdivided into three orders, four families, six genera and includes about 100 species [3]. The most studied family to date Mycoplasmatacae, which includes 2 types: Ureaplasma And Mycoplasma. Man is the natural host for at least 12 mycoplasma species: M. buccalae, M. faucium, M. ferments, M. genitalium, M. hominis, M. incognitis, M. lipophilium, M. pneumoniae, M. orale, M. salivarium, M. urealyticum, M. primatum.

It is believed that all known mobile mycoplasmas are pathogenic for humans and animals. M. pneumoniae - causative agent of respiratory mycoplasmosis, M. incognitis - generalized, poorly understood infectious process, M.ferments plays a role in the development of AIDS, M.hominis.M.urealyticum are causative agents of inflammatory diseases of the urogenital tract.

M.gallisepticum causes various inflammatory diseases of the respiratory tract, joints and nervous system in chickens and turkeys. M.genitalium causes an inflammatory reaction of the urogenital tract not only in humans, but also in monkeys. M.mobile was isolated from fish gills and contributed to the appearance of hemorrhagic and necrotic skin changes [3].

Structure and morphology of mycoplasmas, pathogenicity factors

It is interesting to note that the structure of mycoplasma colonies is extremely diverse and in its form can be represented by numerous elements: small rods, cocci-like cells, spherical bodies of different optical density, filamentous and branched structures of different lengths. Obviously, due to the variety of forms of mycoplasma,

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