A bacterial cell lacks a nucleus; chromosomes are freely located in the cytoplasm. In addition, the bacterial cell lacks membrane organelles: mitochondria, EPS, Golgi apparatus, etc. The outside of the cell membrane is covered with a cell wall.

Most bacteria move passively, using water or air currents. Only some of them have organelles of movement - flagella. Prokaryotic flagella are very simple in structure and consist of the flagellin protein, which forms a hollow cylinder with a diameter of 10–20 nm. They screw into the medium, propelling the cell forward. Apparently, this is the only structure known in nature that uses the wheel principle.

Based on their shape, bacteria are divided into several groups:

Cocci (have a round shape);
- bacilli (have a rod-shaped form);
- spirilla (have the shape of a spiral);
- vibrios (comma-shaped).

According to the method of respiration, bacteria are divided into aerobes (most bacteria) and anaerobes (the causative agents of tetanus, botulism, gas gangrene). The former need oxygen to breathe; for the latter, oxygen is useless or even poisonous.

The protoplasm of bacteria, like that of eukaryotes, is surrounded by a plasma membrane. Saccular, tubular or lamellar invaginations of the membrane contain mesosomes involved in the respiration process, bacteriochlorophyll and other pigments.

The genetic material of prokaryotes does not form a nucleus, but is located directly in the cytoplasm. Bacterial DNA is a single circular molecule, each of which consists of thousands and millions of nucleotide pairs. The genome of a bacterial cell is much simpler than that of the cells of more developed creatures: on average, bacterial DNA contains several thousand genes.

In prokaryotic cells there is no endoplasmic reticulum, and ribosomes float freely in the cytoplasm. Prokaryotes do not have mitochondria; Their functions are partially performed by the cell membrane.

The mobility of bacteria is ensured by flagella. Bacteria reproduce by dividing approximately every 20 minutes (under favorable conditions). DNA is replicated, with each daughter cell receiving its own copy of the parent DNA. It is also possible to transfer DNA between non-dividing cells (by capturing “naked” DNA, using bacteriophages, or by conjugation, when bacteria are connected to each other by copulation fimbriae), but this does not increase the number of individuals. Reproduction is prevented by the sun's rays and the products of their own vital activity.

The behavior of bacteria is not particularly complex. Chemical receptors record changes in the acidity of the environment and the concentration of various substances: sugars, amino acids, oxygen. Many bacteria respond to changes in temperature or light, and some bacteria can sense the Earth's magnetic field. Under unfavorable conditions, the bacterium becomes covered with a dense shell, the cytoplasm is dehydrated, and vital activity almost ceases. In this state, bacterial spores can remain in a deep vacuum for hours and tolerate temperatures from –240 °C to +100 °C.

Microorganisms (microbes) are single-celled organisms smaller than 0.1 mm in size that cannot be seen with the naked eye. These include bacteria, microalgae, some lower filamentous fungi, yeast, and protozoa (Fig. 1). Microbiology studies them.

Rice. 1. Microbiology objects.

In Fig. 2. You can see some representatives of single-celled protozoa. Sometimes the objects of this science include the most primitive organisms on Earth - viruses that do not have a cellular structure and are complexes of nucleic acids (genetic material) and protein. More often they are isolated into a completely separate field of study (Virology), since microbiology is rather aimed at the study of microscopic single-celled organisms.

Rice. 2. Individual representatives of unicellular eukaryotes (protozoa).

The sciences of algology and mycology, which study algae and fungi, respectively, are separate disciplines that overlap with microbiology in the study of microscopic living objects. Bacteriology is a true branch of microbiology. This science deals exclusively with the study of prokaryotic microorganisms (Fig. 3).

Rice. 3. Scheme of a prokaryotic cell.

Unlike eukaryotes, which include all multicellular organisms, as well as protozoa, microscopic algae and fungi, prokaryotes do not have a formed nucleus containing genetic material and real organelles (permanent specialized structures of the cell).

Prokaryotes include true bacteria and archaea, which according to modern classification are designated as domains (superkingdoms) Archaea and Eubacteria (Fig. 4).

Rice. 4. Domains of modern biological classification.

Structural features of bacteria

Bacteria are an important link in the cycle of substances in nature; they decompose plant and animal residues, clean bodies of water contaminated with organic matter, and modify inorganic compounds. Without them, life on earth could not exist. These microorganisms are distributed everywhere, in soil, water, air, animal and plant organisms.

Bacteria differ in the following morphological features:

1. Cell shape (round, rod-shaped, filamentous, convoluted, spiral, as well as various transitional options and star-shaped configuration).
2. The presence of devices for movement (immobile, flagellated, due to the secretion of mucus).
3. Articulation of cells with each other (isolated, linked in the form of pairs, granules, branching forms).

Among the structures formed by round bacteria (cocci), there are cells that are in pairs after division and then break up into single formations (micrococci) or remain together all the time (diplococci). A quadratic structure of four cells is formed by tetracocci, a chain by streptococci, a granule of 8-64 units by sarcina, and clusters by staphylococci.

Rod-shaped bacteria are represented by a variety of shapes due to the great variability in the length (0.1-15 µm) and thickness (0.1-2 µm) of the cell. The shape of the latter also depends on the ability of bacteria to form spores - structures with a thick shell that allows microorganisms to survive unfavorable conditions. Cells with this ability are called bacilli, and those without such properties are simply called rod-shaped bacteria.

Special modifications of rod-shaped bacteria are filamentous (elongated) forms, chains and branching structures. The latter is formed by actinomycetes at a certain stage of development. “Curved” rods are called crimped bacteria, among which vibrios are isolated; spirilla having two bends (15-20 µm); spirochetes that resemble wavy lines. Their cell lengths are 1-3, 15-20 and 20-30 µm, respectively. In Fig. Figures 5 and 6 show the main morphological forms of bacteria, as well as the types of spore arrangement in the cell.

Rice. 5. Basic forms of bacteria.

Rice. 6. Bacteria according to the type of spore location in the cell. 1, 4 – in the center; 2, 3, 5 – end location; 6 – from the side.

The main cellular structures of bacteria: nucleoid (genetic material), ribosomes intended for protein synthesis, cytoplasmic membrane (part of the cell membrane), which in many representatives is additionally protected from above, capsule and mucous sheath (Fig. 7).

Rice. 7. Scheme of a bacterial cell.

According to the classification of bacteria, there are more than 20 types. For example, extremely thermophilic (high temperature lovers) Aquificae, anaerobic rod-shaped bacteria Bacteroidetes. However, the most dominant phylum, which includes diverse representatives, is Actinobacteria. It includes bifidobacteria, lactobacilli, and actinomycetes. The uniqueness of the latter lies in the ability to form mycelium at a certain stage of development.

In common parlance this is called mycelium. Indeed, the branching cells of actinomycetes resemble fungal hyphae. Despite this feature, actinomycetes are classified as bacteria, since they are prokaryotes. Naturally, their cells are less similar in structure to fungi.

Actinomycetes (Fig. 8) are slow-growing bacteria, and therefore do not have the ability to compete for readily available substrates. They are capable of decomposing substances that other microorganisms cannot use as a carbon source, in particular petroleum hydrocarbons. Therefore, actinomycetes are intensively studied in the field of biotechnology.

Some representatives concentrate in areas of oil fields, and create a special bacterial filter that prevents the penetration of hydrocarbons into the atmosphere. Actinomycetes are active producers of practically valuable compounds: vitamins, fatty acids, antibiotics.

Rice. 8. Representative actinomycete Nocardia.

Fungi in microbiology

The object of microbiology is only lower mold fungi (rhizopus, mucor, in particular). Like all mushrooms, they are not able to synthesize substances themselves and require a nutrient medium. The mycelium of the lower representatives of this kingdom is primitive, not divided by partitions. A special niche in microbiological research is occupied by yeast (Fig. 9), characterized by the absence of mycelium.

Rice. 9. Forms of colonies of yeast cultures on a nutrient medium.

Currently, much knowledge has been collected about their beneficial properties. However, yeast continues to be studied for its ability to synthesize practically valuable organic compounds and is actively used as model organisms in genetic experiments. Since ancient times, yeast has been used in fermentation processes. Metabolism differs among different representatives. Therefore, some yeasts are more suitable for a particular process than others.

For example, Saccharomyces beticus, which is more resistant to high alcohol concentrations, is used to create strong wines (up to 24%). While, the yeast S. cerevisiae is able to produce lower concentrations of ethanol. According to the areas of their application, yeasts are classified into feed, bakers, brewers, spirits, and wines.

Pathogenic microorganisms

Disease-causing or pathogenic microorganisms are found everywhere. Along with well-known viruses: influenza, hepatitis, measles, HIV, etc., dangerous microorganisms are rickettsia, as well as streptococci and staphylococci, which cause blood poisoning. Among rod-shaped bacteria there are many pathogens. For example, diphtheria, tuberculosis, typhoid fever (Fig. 10). Many representatives of microorganisms dangerous to humans are found among protozoa, in particular malarial plasmodium, toxoplasma, leishmania, lamblia, trichomonas, and pathogenic amoebas.

Rice. 10. Photo of the bacterium Bacillus anthracis, which causes anthrax.

Many actinomycetes are not dangerous to humans and animals. However, many pathogenic representatives are found among mycobacteria that cause tuberculosis and leprosy. Some actinomycetes initiate a disease such as actinomycosis, accompanied by the formation of granulomas and sometimes an increase in body temperature. Certain types of mold fungi are capable of producing substances toxic to humans - mycotoxins. For example, some representatives of the genus Aspergillus, Fusarium. Pathogenic fungi cause a group of diseases called mycoses. Thus, candidiasis or, simply put, thrush is caused by yeast-like fungi (Fig. 11). They are always present in the human body, but are activated only when the immune system is weakened.

Rice. 11. Candida fungus is the causative agent of thrush.

Fungi can cause a variety of skin lesions, in particular all kinds of lichen, except for herpes zoster, which is caused by a virus. Malassezia yeast, permanent inhabitants of human skin, can cause a decrease in the activity of the immune system. Don't immediately rush to wash your hands. Yeasts and opportunistic bacteria in good health perform an important function, preventing the development of pathogens.

Viruses as an object of microbiology

Viruses are the most primitive organisms on earth. In a free state, no metabolic processes occur in them. Only when they enter a host cell do viruses begin to multiply. In all living organisms, the carrier of genetic material is deoxyribonucleic acid (DNA). Only among viruses are there representatives with a genetic sequence such as ribonucleic acid (RNA).

Viruses are often not classified as truly living organisms.

The morphology of viruses is very diverse (Fig. 12). Typically, their diametrical sizes range from 20-300 nm.

Rice. 12. Diversity of viral particles.

Some representatives reach a length of 1-1.5 microns. The structure of the virus consists of surrounding the genetic material with a special protein frame (capsid), characterized by a variety of shapes (helical, icosahedral, spherical). Some viruses also have an envelope on top formed from the host cell membrane (supercapsid). For example, (Fig. 13) is known as the causative agent of a disease called (AIDS). It contains RNA as genetic material and affects a certain type of immune system cell (helper T-lymphocytes).

Rice. 13. Structure of the human immunodeficiency virus.

Concept of microorganisms

Microorganisms- these are organisms invisible to the naked eye due to their small size.

The size criterion is the only one that unites them.

Otherwise, the world of microorganisms is even more diverse than the world of macroorganisms.

According to modern taxonomy, microorganisms to 3 kingdoms:

• Vira - viruses;
• Eucariotae - protozoa and fungi;
• Procariotae - true bacteria, rickettsia, chlamydia, mycoplasma, spirochetes, actinomycetes.

Just like for plants and animals, the name of microorganisms is used binary nomenclature, i.e., generic and specific name.

If researchers cannot determine species affiliation and only genus affiliation is determined, then the term species is used. Most often this occurs when identifying microorganisms that have non-traditional nutritional needs or living conditions. Genus name usually either based on the morphological characteristic of the corresponding microorganism (Staphylococcus, Vibrio, Mycobacterium), or is derived from the name of the author who discovered or studied the pathogen (Neisseria, Shigella, Escherichia, Rickettsia, Gardnerella).

Species name often associated with the name of the main disease caused by this microorganism (Vibrio cholerae - cholera, Shigella dysenteriae - dysentery, Mycobacterium tuberculosis - tuberculosis) or with the main habitat (Escherihia coli - E. coli).

In addition, in Russian-language medical literature it is possible to use the corresponding Russified name of bacteria (instead of Staphylococcus epidermidis - epidermal staphylococcus; Staphylococcus aureus - Staphylococcus aureus, etc.).

Kingdom of prokaryotes

includes the department of cyanobacteria and the department of eubacteria, which, in turn, divided intoorders:

• bacteria themselves (divisions Gracilicutes, Firmicutes, Tenericutes, Mendosicutes);
• actinomycetes;
• spirochetes;
• rickettsia;
• chlamydia.

Orders are divided into groups.

Prokaryotes differ from eukaryotes because Dont Have:

• morphologically formed nucleus (no nuclear membrane and no nucleolus), its equivalent is a nucleoid, or genophore, which is a closed circular double-stranded DNA molecule attached at one point to the cytoplasmic membrane; by analogy with eukaryotes, this molecule is called a chromosomal bacterium;
• Golgi reticular apparatus;
• endoplasmic reticulum;
• mitochondria.

There is also a number of signs or organelles, characteristic of many, but not all prokaryotes, which allow distinguish them from eukaryotes:

• numerous invaginations of the cytoplasmic membrane, which are called mesosomes, they are associated with the nucleoid and are involved in cell division, sporulation and respiration of the bacterial cell;
• a specific component of the cell wall is murein; its chemical structure is peptidoglycan (diaminopiemic acid);
• Plasmids are autonomously replicating circular molecules of double-stranded DNA with a molecular weight lower than that of a bacterial chromosome. They are located along with the nucleoid in the cytoplasm, although they can be integrated into it, and carry hereditary information that is not vital for the microbial cell, but provides it with certain selective advantages in the environment.

Most famous:

F-plasmids providing conjugative transfer

between bacteria;

R-plasmids are drug resistance plasmids that ensure the circulation among bacteria of genes that determine resistance to chemotherapeutic agents used to treat various diseases.

Bacteria

Prokaryotic, predominantly unicellular microorganisms that can also form associations (groups) of similar cells, characterized by cellular, but not organismal, similarities.

Basic taxonomic criteria,allowing to classify bacterial strains into one group or another:

• morphology of microbial cells (cocci, rods, convoluted);
• relation to Gram staining - tinctorial properties (gram-positive and gram-negative);
• type of biological oxidation - aerobes, facultative anaerobes, obligate anaerobes;
• ability to form spores.

Further differentiation of groups into families, genera and species, which are the main taxonomic category, is carried out based on the study of biochemical properties. This principle forms the basis for the classification of bacteria given in special manuals - determinants of bacteria.

View is an evolutionarily established set of individuals having a single genotype, which under standard conditions is manifested by similar morphological, physiological, and biochemical characteristics.

For pathogenic bacteria, the definition of “species” is supplemented by the ability to cause certain nosological forms of diseases.

Exists intraspecific differentiation of bacteriaonoptions:

• according to biological properties - biovars or biotypes;
• biochemical activity - enzyme digesters;
• antigenic structure - serovars or serots;
• sensitivity to bacteriophages - phagevars or phagetypes;
• antibiotic resistance - resistant products.

In microbiology, special terms are widely used - culture, strain, clone.

Culture is a collection of bacteria visible to the eye on nutrient media.

Cultures can be pure (a set of bacteria of one species) or mixed (a set of bacteria of 2 or more species).

Strain is a collection of bacteria of the same species isolated from different sources or from the same source at different times.

Strains may differ in some characteristics that do not go beyond the characteristics of the species. Clone is a collection of bacteria that are the offspring of one cell.

People are trying to find new ways to protect themselves from their harmful influence. But there are also beneficial microorganisms: they promote the ripening of cream, the formation of nitrates for plants, decompose dead tissue, etc. Microorganisms live in water, soil, air, on the body of living organisms and inside them.

Shapes of bacteria

There are main 4 forms of bacteria, namely:

1. Micrococci – located separately or in irregular clusters. They are usually motionless.
2. Diplococci are arranged in pairs and can be surrounded by a capsule in the body.
3. Streptococci occur in the form of chains.
4. Sarcines form clusters of cells shaped like packets.
5. Staphylococci. As a result of the division process, they do not diverge, but form clusters (clusters).

The bacterium has a complex structure:

• Wall cells protect a single-celled organism from external influences, give it a certain shape, provide nutrition and preserve its internal contents.
• Cytoplasmic membrane contains enzymes, participates in the process of reproduction and biosynthesis of components.
• Cytoplasm serves to perform vital functions. In many species, the cytoplasm contains DNA, ribosomes, various granules, and a colloidal phase.
• Nucleoid is the irregularly shaped nuclear region in which DNA is located.
• Capsule is a surface structure that makes the shell more durable and protects against damage and drying out. This mucous structure is more than 0.2 microns thick. With a smaller thickness it is called microcapsule. Sometimes around the shell there is slime, has no clear boundaries and is soluble in water.
• flagella are called surface structures that serve to move cells in a liquid environment or on a solid surface.
• Drank- thread-like formations, much thinner and fewer flagella. They come in various types, differ in purpose and structure. Pili are needed to attach the organism to the affected cell.
• Controversy. Sporulation occurs when unfavorable conditions arise and serves to adapt the species or preserve it.

We suggest considering the main types of bacteria:

Nutrients enter the cell through its entire surface. Microorganisms have become widespread due to the existence of different types of nutrition. To live, they need a variety of elements: carbon, phosphorus, nitrogen, etc. The supply of nutrients is regulated using a membrane.

The type of nutrition is determined by how carbon and nitrogen are absorbed and by the type of energy source. Some of them can obtain these elements from the air and use solar energy, while others require substances of organic origin to exist. They all need vitamins and amino acids that can act as catalysts for reactions occurring in their body. The removal of substances from the cell occurs through the process of diffusion.

In many types of microorganisms, oxygen plays an important role in metabolism and respiration. As a result of respiration, energy is released, which they use to form organic compounds. But there are bacteria for which oxygen is lethal.

Reproduction occurs by dividing the cell into two parts. After it reaches a certain size, the separation process begins. The cell elongates and a transverse septum is formed in it. The resulting parts disperse, but some species remain connected and form clusters. Each of the newly formed parts feeds and grows as an independent organism. When placed in a favorable environment, the reproduction process occurs at high speed.

Microorganisms are able to decompose complex substances into simple ones, which can then be used again by plants. Therefore, bacteria are indispensable in the cycle of substances; without them, many important processes on Earth would be impossible.

Do you know?

Conclusion: Don't forget to wash your hands every time you come home after going outside. When you go to the toilet, also wash your hands with soap. A simple rule, but so important! Keep it clean and bacteria won't bother you!

To reinforce the material, we invite you to complete our exciting assignments. Good luck!

Task No. 1

Look carefully at the picture and tell me which of these cells is bacterial? Try to name the remaining cells without looking at the clues:

2.2. Classification and morphology of bacteria

Classification of bacteria. The decision of the International Code for bacteria recommended the following taxonomic categories: class, division, order, family, genus, species. The species name corresponds to binary nomenclature, i.e. it consists of two words. For example, the causative agent of syphilis is written as Treponema pallidum. The first word is na-

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: T.pallidum.

Bacteria are prokaryotes, i.e. prenuclear organisms, since they have a primitive nucleus without a shell, nucleolus, or histones. and the cytoplasm lacks highly organized organelles (mitochondria, Golgi apparatus, lysosomes, etc.)

In the old Bergey Manual of Systematic Bacteriology, bacteria were divided according to the characteristics of the bacterial cell wall into 4 divisions: Gracilicutes - eubacteria with a thin cell wall, gram-negative; Firmicutes - eubacteria with a thick cell wall, gram-positive; Tenericutes - eubacteria without a cell wall; Mendosicutes - archaebacteria with a defective cell wall.

Each department was divided into sections, or groups, based on Gram staining, cell shape, oxygen demand, motility, metabolic and nutritional characteristics.

According to the 2nd edition (2001) of the ManualBergey, bacteria are divided into 2 domains:"Bacteria" and "Archaea" (Table 2.1).

Table. Domain characteristicsBacteriaAndArchaea

*Among thin-walled gram-negative eubacteria distinguish:

spherical forms, or cocci (gonococci, meningococci, veillonella);

convoluted forms - spirochetes and spirilla;

rod-shaped forms, including rickettsia.

** To thick-walled gram-positive eubacteria include:

spherical forms, or cocci (staphylococci, streptococci, pneumococci);

rod-shaped forms, as well as actinomycetes (branching, filamentous bacteria), corynebacteria (club-shaped bacteria), mycobacteria and bifidobacteria (Fig. 2.1).

Most gram-negative bacteria are grouped into the phylum Proteobacteria. based on similarity in ribosomal RNA “Proteobacteria” - named after the Greek god Proteus. taking on various forms). They appeared from common photosynthesis tic ancestor.

Gram-positive bacteria, according to the studied ribosomal RNA sequences, are a separate phylogenetic group with two large subdivisions - with a high and a low ratio G+ C (genetic similarity). Like the Proteobacteria, this group is metabolically diverse.

To domain "Bacteria» includes 22 types, from whichThe following are of major medical importance:

TypeProteobacteria

Class Alphaproteobacteria. Childbirth: Rickettsia, Orientia, Ehrlichia, Bartonella, Brucella

Class Betaproteobacteria. Childbirth: Burkholderia, Alcaligenes, Bordetella, Neisseria, Kingella, Spirillum

Class Gammaproteobacteria. Childbirth: Francisella, Legionella, Coxiella, Pseudomonas, Moraxella, Acinetobacter, Vibrio, Enterobacter, Callimatobacterium, Citrobacter, Edwardsiella, Erwinia, Escherichia, Hafnia, Klebsiella, Morganella, Proteus, Providencia, Salmonella, Serratia, Shigella, Yersinia, Pasteurella

Class Deltaproteobacteria. Genus: Bilophila

Class Epsilonproteobacteria. Childbirth: Campylobacter, Helicobacter, Wolinella

TypeFirmicutes (mainwaygrampolo­ resident)

Class Clostridia. Childbirth: Clostridium, Sarcina, Peptostreptococcus, Eubacterium, Peptococcus, Veillonella (Gram-negative)

Class Mollicutes. Genera: Mycoplasma, Ureaplasma

Class Bacilli. Childbirth: Bacillus, Sporosarcina, Listeria, Staphylococcus, Gemella, Lactobacillus, Pediococcus, Aerococcus, Leuconostoc, Streptococcus, Lactococcus

TypeActinobacteria

Class Actinobacteria. Childbirth: Actinomyces, Arcanodacterium, Mobiluncus, Micrococcus, Rothia, Stomatococcus, Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, Bifidobacterium, Gardnerella

TypeClamydiae

Class Clamydiae. Childbirth: Clamydia, Clamydophila

TypeSpirochaetes

Class Spirochaetes. Childbirth: Spirochaeta, Borrelia, Treponema, Leptospira

Phylum Bacteroidetes

Class Bacteroidetes. Childbirth: Bacteroides, Porphyromonas, Prevotella

Class Flavobacteria. Childbirth: Flavobacterium

The division of bacteria according to the structural features of the cell wall is associated with the possible variability of their coloring in one color or another using 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. However, it turned out that bacteria with the so-called gram-positive type of cell wall (thicker than that of gram-negative bacteria), for example, bacteria of the genus Mobiluncus and some spore-forming bacteria, instead of the usual gram-positive color, have a gram-negative color. Therefore, for the taxonomy of bacteria, the structural features and chemical composition of cell walls are of greater importance than Gram staining.

2.2.1. Shapes of bacteria

There are several main forms of bacteria (see Fig. 2.1) - coccoid, rod-shaped, convoluted and branching, filamentous forms of bacteria.

Spherical forms, or cocci,- spherical bacteria 0.5-1.0 microns in size*, which, according to their relative positions, are divided into micrococci, diplococci, streptococci, tetracocci, sarcinae And staphylococci.

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

Diplococcus(from Greek diploos - double), or paired cocci, are located in pairs (pneumococcus, gonococcus, meningococcus), since the cells do not separate after division. Pneumococcus (the causative agent of pneumonia) has a lanceolate shape on opposite sides, and gonococcus(the causative agent of gonorrhea) and meningococcus (the causative agent of epidemic meningitis) have the shape of coffee beans, with their concave surface facing each other.

Streptococci(from Greek streptos - chain) - round or elongated cells that form a chain due to cell division in the same plane and the preservation of the connection between them at the site of division.

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

Staphylococcus(from 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 cell ends and relative position of cells. The length of the cells varies from 1.0 to 10 µm, thickness - from 0.5 to 2.0 µm. The rods can be regular (E. coli, etc.) and irregular (corynebacteria And other) forms, including branching ones, for example, in actinomycetes. The smallest rod-shaped bacteria include rickettsia.

The ends of the rods can be cut off (anthrax bacillus), rounded (Escherichia coli), pointed (fusobacteria) or in the form of a thickening. In the latter case, the rod looks like a club (Corynebacterium diphtheria).

The slightly curved rods are called vibrios (Vibrio cholerae). Most rod-shaped bacteria are arranged randomly because the cells move apart after dividing. If after cell division the cells remain connected,

If they share common fragments of the cell wall and do not diverge, they are located at an angle to each other (Corynebacterium diphtheria) or form a chain (anthrax bacillus).

Twisted Shapes- spiral-shaped bacteria, for example spirilla, having the appearance of corkscrew-shaped convoluted cells. Pathogenic spirilla includes the causative agent sodoku (rat bite disease). The convoluted ones also include Campilobacter and Helicobacter, which have bends like the wing of a flying seagull; bacteria such as spirochetes are also close to them. Spirochetes- thin, long, crimped

spiral-shaped) bacteria that differ from spirilla in mobility due to flexural changes in cells. Spirochetes consist of an outer membrane

cell wall) surrounding a protoplasmic cylinder with a cytoplasmic membrane and an axial filament (axistyl). The axial filament is located under the outer membrane of the cell wall (in the periplasm) and, as it were, twists around the protoplasmic cylinder of the spirochete, giving it a helical shape (primary curls of the spirochete). The axial filament consists of periplasmic fibrils - analogues of bacterial flagella and is a contractile protein flagellin. The fibrils are attached to the ends of the cell (Fig. 2.2) and are directed towards each other. The other end of the fibrils is free. The number and arrangement of fibrils varies among species. Fibrils are involved in the movement of spirochetes, giving the cells rotational, bending and translational motion. In this case, spirochetes form loops, curls, and bends, which are called secondary curls. Spirochetes

do not accept dyes well. They are usually painted according to Romanovsky-Giemsa or silver plated. Live spirochetes are examined using phase-contrast or dark-field microscopy.

Spirochetes are represented by 3 genera that are pathogenic for humans: Treponema, Borrelia, Leptospira.

Treponema(genus Treponema) have the appearance of thin, corkscrew-twisted threads with 8-12 uniform small curls. Around the protoplast of the treponema there are 3-4 fibrils (flagella). The cytoplasm contains cytoplasmic filaments. Pathogenic representatives are T.pallidum - the causative agent of syphilis, T.pertenue - causative agent of the tropical disease yaws. There are also saprophytes - inhabitants of the human oral cavity and the 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 (IN.recurrentis) and the causative agents of Lyme disease (IN.burgdorferi and etc.).

Leptospira(genus Leptospira) They have shallow and frequent curls - 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 on the appearance of letters S or with; have 2 axial filaments (flagella). Pathogenic representative L. in­ terrogans causes leptospirosis when ingested with water or food, leading to the development of hemorrhages and jaundice.

in the cytoplasm, and some in the nucleus of infected cells. They live in arthropods (lice, fleas, ticks) that are their hosts or carriers. Rickettsia received its name from H. T. Ricketts, an American scientist who first described one of the pathogens (Rocky Mountain spotted fever). The shape and size of rickettsia may vary (irregular, filamentous cells) depending on growth conditions. The structure of rickettsia does not differ from that of gram-negative bacteria.

Rickettsia have a metabolism independent of the host cell, however, it is possible that they receive high-energy compounds from the host cell for their reproduction. In smears and tissues they are stained according to Romanovsky-Giemsa, according to Macchiavello-Zdrodovsky (rickettsia are red, and infected cells are blue).

In humans, rickettsiae cause epidemic typhus. (Rickettsia prowazekii), tick-borne rickettsiosis (R. sibirica), Rocky Mountain spotted fever (R. rickettsii) and other rickettsioses.

Elementary bodies enter the epithelial cell by endocytosis with the formation of an intracellular vacuole. Inside the cells, they enlarge and transform into dividing reticular bodies, forming clusters in vacuoles (inclusions). Elementary bodies are formed from reticular bodies, which leave the cells by exocytosis or cell lysis. Those who left

Elementary body cells enter a new cycle, infecting other cells (Fig. 16.11.1). 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 Greek. actis - Ray, mykes - fungus) they received due to the formation of drusen in the affected tissues - granules of tightly intertwined threads in the form of rays extending from the center and ending in flask-shaped thickenings. Actinomycetes, like fungi, form mycelium - thread-like intertwining cells (hyphae). They form substrate mycelium, which is formed as a result of cell ingrowth into the nutrient medium, and aerial mycelium, which grows on the surface of the medium. Actinomycetes can divide by fragmentation of the mycelium into cells similar to rod-shaped and cocci-shaped bacteria. On the 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 nocardi-like (nocardioform) actinomycetes, a collective group of rod-shaped, irregularly shaped bacteria. Their individual representatives form branching forms. These include bacteria of the genera Corynebacterium, Mycobacterium, Nocardianjxp. Nocardi-like actinomycetes are distinguished by the presence in the cell wall of the sugars 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-Neelsen, they are red, and non-acid-resistant bacteria and tissue elements, sputum are blue).

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

Cell wall- a strong, elastic structure that gives the bacterium a certain shape and, together with the underlying cytoplasmic membrane, “restrains” the 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 is found in gram-positive bacteria (Fig. 2.4 and 2.5). 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.

Mycoplasmas- small bacteria (0.15-1.0 µm), surrounded only by a cytoplasmic membrane. They belong to the class Mollicutes, contain sterols. Due to the absence of a cell wall, mycoplasmas are osmotically sensitive. They have a variety of shapes: coccoid, filamentous, flask-shaped. These forms are visible during phase-contrast microscopy of pure mycoplasma cultures. On a dense nutrient medium, mycoplasmas form colonies that resemble fried eggs: a central opaque part immersed in the medium and a translucent periphery in the form of a circle.

Mycoplasmas cause atypical pneumonia in humans (Mycoplasma pneumoniae) and lesions of the genitourinary tract (M.homi- nis and etc.). Mycoplasmas cause diseases not only in animals, but also in plants. Non-pathogenic representatives are also quite widespread.

2.2.2. Bacterial cell structure

The structure of bacteria has been well studied using electron microscopy of whole cells and their thin sections, as well as other methods. The bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the shell is protoplasm, consisting of cytoplasm with inclusions and a nucleus called the nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili (Fig. 2.3). Some bacteria are capable of forming spores under unfavorable conditions.

In the cell wall of gram-positive bacteria contains small amounts of polysaccharides, lipids, and proteins. The main component of the cell wall of these bacteria is multilayer peptidoglycan (mu-rein, mucopeptide), accounting for 40-90% of the mass of the cell wall. Teichoic acids (from the Greek. teichos - wall), the molecules of which are chains of 8-50 glycerol and ribitol residues connected by phosphate bridges. The shape and strength of bacteria is given by the rigid fibrous structure of the multilayer peptidoglycan, cross-linked with peptides.

Peptidoglycan is represented by parallel molecules glycan. consisting of repeating N-acetylglucosamine and N-acetylmuramic acid residues connected by a glycosidic bond. These bonds are broken by lysozyme, which is an acetylmuramidase. Glycan molecules are linked through N-acetylmuramic acid by a four-amino acid peptide cross-link ( tetrapeptide). Hence the name of this polymer - peptidoglycan.

The basis of the peptide bond of peptidoglycan in gram-negative bacteria is tetrapeptides consisting of alternating L- and D-amino acids, for example: L-alanine - D-glutamic acid - meso-diaminopimelic acid - D-alanine. U E.coli (gram-negative bacterium) peptide chains are connected to each other through D-alanine of one chain and meso-diaminopimeli-

new acid - another. The composition and structure of the peptide part of the peptidoglycan of gram-negative bacteria is stable, in contrast to the peptidoglycan of gram-positive bacteria, the amino acids of which may differ in composition and sequence. Peptidoglycan tetrapeptides in gram-positive bacteria are connected to each other by polypeptide chains of 5 residues

glycine (pentaglycine). Instead of meso-diamino-pimelic acid, they often contain lysine. Glycan elements (acetylglucosamine and acetylmuramic acid) and tetra-peptide amino acids (meso-diaminopimelic and D-glutamic acids, D-alanine) are a distinctive feature of bacteria, since they are absent in animals and humans.

The ability of Gram-positive bacteria to retain gentian violet in combination with iodine when stained using Gram stain (blue-violet color of bacteria) is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, subsequent treatment of a bacterial smear with alcohol causes a narrowing of the pores in the peptidoglycan and thereby retains the dye in the cell wall. Gram-negative bacteria lose the dye after exposure to alcohol, which is due to a smaller amount of peptidoglycan (5-10% of the cell wall mass); they are discolored with alcohol and, when treated with fuchsin or safranin, acquire a red color.

IN composition of the cell wall of gram-negative bacteria enters the outer membrane, connected via lipoprotein to the underlying layer of peptidoglycan (Fig. 2.4 and 2.6). When viewed by electron microscopy of ultrathin sections of bacteria, the outer membrane has the appearance of a wavy three-layer structure, similar to the inner membrane, which is called cytoplasmic. The main component of these membranes is a bimolecular (double) layer of lipids.

The outer membrane is a mosaic structure represented by lipopolysaccharides, phospholipids and proteins. Its inner layer is represented by phospholipids, and the outer layer contains lipopolysaccharide(LPS). Thus, the outer membrane is asymmetrical. The outer membrane LPS consists of three fragments:

lipid A - a conservative structure, almost the same in gram-negative bacteria;

core, or core, crustal part (lat. core - core), relatively conserved 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 causes 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. The core, or core part, of LPS extends from lipid A. The most constant part of the LPS core is keto-deoxyoctonic acid (3-deoxy-O-man-no-2-octulosonic acid). The O-specific chain extending from the core part of the LPS molecule determines the serogroup, serovar (a type of bacteria detected by immune serum) of a particular strain of bacteria. Thus, the concept of LPS is associated with the concept of O-antigen, by which bacteria can be differentiated. Genetic changes can lead to defects, “shortening” of bacterial LPS and the resulting “rough” colonies of R-forms.

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

Between the outer and cytoplasmic membrane there is a periplasmic space, or periplasm, containing enzymes (proteases, lipases, phosphatases,

nucleases, beta-lactamases), as well as components of transport systems.

When the synthesis of the bacterial cell wall is disrupted under the influence of lysozyme, penicillin, protective factors of the body and other compounds, cells with a modified (often spherical) shape are formed: protoplasts - bacteria completely devoid of a cell wall; spheroplasts are bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i.e., acquire a full cell wall and restore their original shape.

Bacteria of the sphero- or protoplast type, which have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to reproduce, are called L-forms (from the name of the D. Lister Institute, where they were first 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 bacteria is removed, can reverse, “returning” to the original bacterial cell. L-forms can be produced by many pathogens of infectious diseases.

Cytoplasmic membrane ana in electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers, each 2.5 nm thick, separated by a light intermediate one). In structure (see Fig. 2.5 and 2.6) it is similar to the plasmalemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins that seem to penetrate through the structure of the membrane. Some of them are permeases involved in the transport of substances.

The cytoplasmic membrane is a dynamic structure with mobile components, so it is thought of as a mobile fluid structure. It surrounds the outer part of the bacterial cytoplasm and is involved in the regulation of osmotic pressure.

niya, transport of substances and energy metabolism of the cell (due to enzymes of the electron transport chain, adenosine triphosphatase, etc.).

With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complex twisted membrane structures, called mesosomes. Less complexly twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes is not fully understood. It is even suggested that they are an artifact that occurs after preparing (fixing) a specimen for electron microscopy. Nevertheless, it is believed that derivatives of the cytoplasmic membrane participate in cell division, providing energy for the synthesis of the cell wall, and take part in the secretion of substances and sporulation, i.e., in processes with high energy consumption.

The cytoplasm occupies the main volume of the bacterial cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes, responsible for the synthesis (translation) of proteins.

Bacterial ribosomes have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to SOS ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics, by binding to bacterial ribosomes, inhibit bacterial protein synthesis without affecting protein synthesis in eukaryotic cells. Bacterial ribosomes can dissociate into two subunits - 50S and 30S. Ribosomal RNAs (rRNAs) are conserved elements of bacteria (the “molecular clock” of evolution). 16S rRNA is part of the small ribosomal subunit, and 23S rRNA is part of the large ribosomal subunit. The study of 16S rRNA is the basis of gene systematics, allowing one to assess the degree of relatedness of organisms.

The cytoplasm contains various inclusions in the form of glycogen granules, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin). They accumulate when there is an excess of nutrients in the environment and

They act as reserve substances for nutrition and energy needs.

Volutin has an affinity for basic dyes and is easily detected using special staining methods (for example, Neisser) in the form of metachromatic granules. With toluidine blue or methylene blue, volutin is stained red-violet, and the cytoplasm of the bacterium is stained blue. The characteristic arrangement of volutin granules is revealed in the diphtheria bacillus in the form of intensely stained cell poles. Metachromatic staining of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1-1.0 microns in size.

Nucleoid- equivalent to the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Typically, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring. If division is disrupted, 4 or more chromosomes can converge in it. The nucleoid is detected in a light microscope after staining using DNA-specific methods: Feulgen or Romanovsky-Giemsa. In electron diffraction patterns of ultrathin sections of bacteria, the nucleoid appears as light zones with fibrillar, thread-like structures of DNK bound in certain areas to

cytoplasmic membrane or mesoso-

mine, involved in chromosome replication (see Fig. 2.5 and 2.6).

In addition to the nucleoid, represented by one

chromosome, in a bacterial cell there are

extra-chromosomal factors of heredity -

plasmids (see section 5.1.2.) representing

are covalently closed rings of DNA.

Capsule, microcapsule, mucus . Capsule-

a mucous structure more than 0.2 microns thick, firmly associated with the cell wall of bacteria and having clearly defined external boundaries. The capsule is visible in fingerprint smears from pathological material. In pure cultures of bacteria, a capsule is formed

less often. It is detected using special methods of staining a smear according to Burri-Gins, which creates a negative contrast of the substances of the capsule: 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 and contains a large amount of water. It prevents the phagocytosis of bacteria. Capsule antigen-na: Antibodies against the capsule cause it increase (swelling reaction and I capsule ly).

Many bacteria form a microcapsule - a mucous formation less than 0.2 microns thick, detectable only by electron microscopy. Mucus should be distinguished from the capsule - mucoid exopolysaccharides that do not have clear external boundaries. Mucus 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 glyco-

calix. In addition to the synthesis of exopolysaccharides by bacteria, there is another mechanism for their formation: through the action of extracellular bacterial enzymes on disaccharides. As a result, dextrans and levans are formed.

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

Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself (Fig. 2.7). The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of 3 parts: a spiral filament, a hook and a basal body containing a rod with special disks (1 pair of disks in gram-positive bacteria and 2 pairs in gram-negative bacteria). Flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a rod - a rotor - rotating the flagellum. The proton potential difference on the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The rotation speed of the flagellum can reach 100 rps. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.

Flagella consist of a protein - flagellin (from. flagellum - flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are twisted in a spiral.

The number of flagella in bacteria of various species varies from one (monotrichus) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacterium (peritrichus) in Escherichia coli, Proteus, etc. Lophotrichus have a bundle of flagella at one end of the cell. Amphitrichy has 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 treatment with special methods based on etching and adsorption of various

substances leading to an increase in the thickness of flagella (for example, after silvering).

Villi, or drank(fimbriae) - thread-like formations (Fig. 2.7), thinner and shorter (3 + 10 nm x 0.3 + 10 µm) than flagella. The pili extend from the cell surface and are composed of the protein pilin. They have antigenic activity. There are pili responsible for adhesion, i.e., for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism, and sexual (F-pili), or conjugation pili.

Pili are usually numerous - several hundred per cell. However, she usually has 1-3 sexual saws per cell: they are formed by the so-called “male” donor cells containing transmissible plasmids (F-, R-, Col plasmids). A distinctive feature of the sex pili is their interaction with special “male” spherical bacteriophages, which are intensively adsorbed on the sex pili (Fig. 2.7).

Controversy- a peculiar form of resting bacteria with a gram-positive type of cell wall structure (Fig. 2.8).

Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.). A single spore (endospore) is formed inside a bacterial cell. The formation of spores contributes to the preservation of the species and is not a method of reproduction, like in fungi.

Spore-forming bacteria of the genus Bacillus, y whose spore size 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 shape of a spindle, are called clostridia, for example bacteria of the genus Clostridium (lat. Clostridium - spindle). The spores are acid-resistant, therefore they are stained red using the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell is stained blue.

Sporulation, the shape and location of spores in a cell (vegetative) are a species property of bacteria, which allows them to be distinguished from each other. The shape of the spores can be oval, spherical; 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 the causative agents of botulism, gas gangrene) and central in the anthrax bacillus).

Process sporulation(sporulation) goes through a series of stages, during which part of the cytoplasm and chromosome of the bacterial vegetative cell are separated, surrounded by an growing cytoplasmic membrane - a prospore is formed. The prospore is surrounded by two cytoplasmic membranes, between which a thick modified peptidoglycan layer of cortex (bark) is formed. From the inside it comes into contact with the cell wall of the spore, and from the outside - with the inner shell of the spore. The outer shell of the spore is formed by a vegetative cell. The spores of some bacteria have an additional covering - exosporium. In this way, a multilayer, poorly permeable shell is formed. Sporulation is accompanied by intensive consumption of dipicolic acid and calcium ions by the prospore, and then by the developing spore shell. The dispute 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 multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. In soil, for example, the pathogens of anthrax and tetanus can persist for decades.

Under favorable conditions, spores germinate, going through three successive stages: ac-

motivation, 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 lasts several minutes. The outgrowth stage is characterized by rapid growth, accompanied by the destruction of the shell and the emergence of a seedling.