Introduction

Microbiology is the science of tiny organisms invisible to the naked eye, called microbes or microorganisms. She studies the patterns of their life and development, as well as the changes they cause in the body of people, animals, plants and inanimate nature. The development of microbiology, like other scientific disciplines, is closely dependent on production methods, practical needs, and the general progress of science and technology.

The goal of microbiology as a science is the study of the systematics, morphology (shape and structure) and physiology (life activity) of microorganisms, methods of their isolation and recognition, as well as elucidation of their significance in nature and the possibilities of application in various fields of human activity.

Microbiological control in food production represents all research and control methods related to determining the degree of bacterial contamination of the controlled object, as well as methods for quantitative accounting of microflora.

Morphology of bacteria

Bacteria shape

The vast majority of known bacteria have the shape of either a sphere (spherical), a cylinder (rod-shaped), or a spiral. Spherical bacteria (Fig. 1.) are single (cocci), connected by two cells (diplococci), four cells (tetracocci), in long chains (streptococci), in packets (sarcins), in the form of irregularly shaped clusters (staphylococci) . Rod-shaped bacteria (Fig. 1.) differ in the ratio of cell length to its transverse size. In short rods this ratio is so small that it is difficult to distinguish them from cocci; they are divided into bacteria (not forming spores) and bacilli (forming spores). Spiral-shaped bacteria are characterized by a different number of turns; spirilla have from one to several turns; vibrios look like curved rods; they can be considered as an incomplete turn of a spiral.

With the development of microscopic technology and the improvement of preparation methods, other exotic forms of bacteria have been discovered. Some bacteria have the appearance of a closed or open ring, some have visible cellular outgrowths (prosteks), the number of which ranges from 1 to 8 or more, worm-shaped bacteria similar to crystals have been found, etc.

Structure of a bacterial cell

A bacterial cell has a very complex heterogeneous and at the same time strictly ordered structure. In general terms, the structure of a bacterial cell does not differ from the structure of the cells of higher organisms. The cell, as a universal unit of life, turned out to be such a perfect form of organization of living matter that in the process of evolution from unicellular to higher multicellular organisms, it retained all the main features of its structure, and, consequently, its functions.

Figure 1. Shapes of bacteria. Spherical: a - micrococci, b - streptococci, c - diplococci, d - staphylococci, d - sarcina; rods: e - bacteria, g - bycillus, h,i - convoluted, k - spirillum.

In Fig. 2. A diagram of the structure of a bacterial cell by the famous cytologist V.I. is presented. Turquoise. The shape of a bacterial cell is determined by a rigid (rigid) cell wall, which gives the cell a specific, hereditarily fixed external shape. On the cell wall of bacteria there are so-called surface structures: capsule, flagella, genital villi, cilia. Under the cell wall is the cytoplasmic membrane (CPM), which delimits the cytoplasm of the cell. The cytoplasmic membrane together with the cytoplasm is called a protoplast. All layers located on the outside of the cytoplasmic membrane are called the cell membrane.

Cell wall.

Prokaryotes have a cell wall made of peptidoglycan, which is not found in eukaryotic cells. Depending on the structure of the cell wall, prokaryotes are divided into two groups: gram-positive and gram-negative. This division is based on the difference in the coloring method proposed in 1884 by the Danish scientist H. Gram. The cell walls of gram-positive and gram-negative prokaryotes differ sharply in both chemical composition and ultrastructure.

Rice. 2. Scheme of the structure of a bacterial cell: O - cell membrane; CM - cytoplasmic membrane; M - mitochondrion (mesosome); F - fatty inclusions; NV - nuclear vacuole; DNA - DNA strands; ES - ergastoplasmic system; R - ribosomes; B - volutin; G - glycogen

The cell wall of gram-positive bacteria contains 50... 90% peptidoglycan, gram-negative bacteria - 1... 10% peptidoglycan. In addition to peptidoglycan, the cell wall of gram-positive prokaryotes contains unique chemical compounds - teichoic acids. The cell wall of prokaryotes accounts for 5 to 50% of cell dry matter.

The cell wall of prokaryotes performs various functions: mechanically protects the cell from environmental influences, ensures the maintenance of its external shape, and allows the cell to exist in hypotonic solutions. The cell wall contains channels, or diffusion pores, for the passive transport of substances and ions into the cell.

The cell wall prevents toxic substances from entering the cell. On the outer side of the cell wall there are many macromolecules that come into contact with the environment: specific receptors for phages, antigens, macromolecules that provide intercellular interactions during conjugation, as well as between pathogenic bacteria and cells and tissues of higher organisms.

Surface structures.

Bacteria have a capsule outside the cell wall (Fig. 3.) - a mucous formation that envelops the cell, maintains connection with the cell wall and has an amorphous structure. Depending on the thickness of the capsule, there are microcapsules (thickness less than 0.2 microns) and macrocapsules (thickness greater than 0.2 microns). Capsules protect the cell from mechanical damage and drying out, create an additional osmotic barrier, and serve as an obstacle to the penetration of phages. Sometimes the capsule serves as a source of reserve nutrients. Mucus helps cells attach to various surfaces. Currently, the ability of some bacteria to synthesize capsules (a kind of extracellular polymers) is used in practice as substitutes for blood plasma and for the production of synthetic films.

Fig 3.

Many bacteria are immobile, but if they are able to move, this movement is ensured by flagella - structures located on the surface of cells. The number, size and location of flagella, as a rule, are a constant characteristic for this species (Fig. 4.), and have taxonomic significance. Without flagella, only gliding bacteria and spirochetes are able to move. Typically, the thickness of the flagellum is 15-20 nm, length 3-15 µm. Bacteria with flagella can move very quickly, such as Bac. megaterium at a speed of 16 mm/min, Vibro cholerae - 12 mm/min.

Rice. 4.

With the polar arrangement of the flagella, they act like a ship's propeller and push the cell through the surrounding liquid medium. The rotational movement of the flagellum occurs due to the basal body. The flagella rotate relatively quickly. In spirilla, they rotate at about 3000 rpm, which is close to the speed of an average electric motor. The rotation of the flagella also causes the cell to rotate at 1/3 of this speed in the opposite direction.

The peritrichous flagella of E. coli work as one well-coordinated helical bundle and push the cell through its environment (Fig. 4.).

Study of flagella in an electron microscope showed that they consist of three parts (Fig. 5.). The main mass of the flagellum is a long spiral thread (fibril), which passes at the surface of the cell wall into a thickened curved structure - a hook. The thread is attached with a hook to the basal body, which is a system of two or four rings (L, P, Sw. M) strung on a rod, which is a continuation of the hook.

Rice. 5.

Recently, great strides have been made in deciphering the mechanism of movement of prokaryotes. The prokaryotic cell has a mechanism that allows it to convert electrochemical energy directly into mechanical energy. In addition to flagella, the cell wall of a prokaryotic cell may contain sex villi and cilia in the form of projections of various lengths (Fig. 6).

Rice. 6. Types of E.coli hairs: F - flagella, S - sex villi (F-like sexpili), C - cilia.

Cytoplasmic membrane.

Under the cell wall there is a cytoplasmic membrane, which is an essential structural element of any cell, violation of the integrity of which leads to the loss of cell viability. The CPM accounts for 8...15% of the dry matter of the cell. CPM is a protein-lipid complex and a small amount of carbohydrates.

The CPM performs a variety of functions using special transporters called translocases. A special transfer of various organic and inorganic molecules and ions occurs through the membrane.

Many enzymes are localized in the CPM. The CPM is the main barrier that ensures the selective entry and exit of various substances and ions into the cell.

In prokaryotes, local invaginations of the CPM are described, which are called mesosomes. Mesosomes vary in size, shape and location in the cell. It is believed that mesosomes are associated with increased energy metabolism of cells.

Cytoplasm.

The contents of the cell, surrounded by the CPM, are called cytoplasm. The cytoplasm has a homogeneous consistency and contains a set of soluble RNA, enzymes, products and substrates of metabolic reactions. The cytoplasm contains various structures: ribosomes, genetic apparatus (DNA) and inclusions of different chemical natures and functional purposes.

Ribosomes are ribonucleoprotein particles with a size of 15-20 nm. Their number in a cell depends on the intensity of the protein synthesis process. A rapidly growing Escherichia coli cell contains approximately 15,000 ribosomes. Protein synthesis is carried out by aggregates consisting of ribosomes, messenger and transport RNA molecules, called polyribosomes. The genetic apparatus of a prokaryotic cell is represented by one DNA molecule, which has the shape of a covalently closed ring and is called the bacterial chromosome. The length of an unfolded DNA molecule can be more than 1 mm, i.e. almost 1000 times the length of a bacterial cell. The genetic apparatus of a prokaryotic cell is called a nucleoid.

In the cytoplasm of prokaryotes there are various inclusions, some of which act as reserve nutrients, represented by polysaccharides, lipids, polypeptides, polyphosphates, and sulfur deposits. Polysaccharides are glycogen, starch, granulosa (starch-like substance). They are more common among representatives of anaerobic spore bacteria of the Clostridia group. In unfavorable conditions they are used as sources of carbon and energy. Lipids accumulate in the form of granules consisting of a polymer of β-hydroxybutyric acid. In some prokaryotes that oxidize hydrocarbons, poly-β-hydroxybutyric acid makes up up to 70% of the dry matter of the cell.

Lipids serve as a good source of carbon and energy for the cell. Polyphosphates, which also accumulate in the form of granules, are called volutin and are used by cells as a source of phosphorus. Bacteria that carry out chemosynthesis through the oxidation of hydrogen sulfide are characterized by the accumulation of molecular sulfur in their cells. All accumulated (reserve) substances, presented in the form of high molecular weight polymer molecules, are delimited from the cytoplasm by a protein membrane.

Bacteria pigments

Colonies of many bacteria are brightly colored. The ability to synthesize pigments is determined genetically. Among the bacterial pigments there are carotenoids, phenazine dyes, pyrroles, azaquinones, anthocyanins, etc.

Pigments protect cells from light damage and use light for photosynthesis. In many microorganisms, pigment formation occurs only in light. For example, the bright red color of the colonies of Serratia marcescens is due to the presence of the pigment prodigiosin. The bacteria Pseudomonas indigofem, Cotynebacterium insidiosum, Arthrobacter atrocyaneus and others synthesize indigoidine, a water-insoluble blue pigment released into the medium. Chromobacterium violaceum produces the blue-violet pigment violacein, which is insoluble in water. Violacein is a derivative of indole, formed during the oxidation of tryptophan. Pseudomonas aeruginosa produces the pigment nix-pyocyanin. Various strains of pseudomonads produce pigments such as phenazine-1-carboxylic acid, oxychlorophine, iodinine, and sometimes all pigments together.

All pigments belong to secondary metabolites, i.e. they do not belong to those compounds that are found in all organisms, and are derivatives of ordinary metabolites or structural components of the cell. Some pigments have antibiotic properties, so many pigmented microorganisms are antibiotic producers.

Growth and methods of reproduction of bacteria

The growth of a prokaryotic cell is a coordinated increase in the amount of all the chemical components from which it is built. Growth is the result of many coordinated biosynthetic processes under strict regular control and results in an increase in cell mass and size. Cell growth is not unlimited. After reaching a certain (critical) size, the cell undergoes division. Most prokaryotes are characterized by equal binary transverse division, leading to the formation of two identical daughter cells.

In most gram-positive bacteria, division occurs through the synthesis of a transverse septum running from the periphery to the center. The transverse septum is formed from the CPM and the peptidoglycan layer. The outer layers are synthesized later.

The cells of most gram-negative bacteria divide by constriction. For example, in E. coli, at the site of division, a gradually increasing and inward curvature of the CPM and cell wall is found.

A variant of binary fission is budding, in which a small outgrowth (bud) is formed at one of the poles of the mother cell, which increases in size during growth. Gradually, the bud reaches the size of the mother cell and separates from it. Budding cells undergo senescence. With equal binary fission, the mother cell gives rise to two daughter cells and then disappears. In budding, a mother cell gives rise to a daughter cell and morphological differences can be detected between them. The division of a prokaryotic cell begins, as a rule, some time after the completion of the DNA division cycle.

Bacterial sporulation

To withstand unfavorable conditions, vegetative cells of many prokaryotes form special cells (endospores) that have increased resistance. Morphological differentiation is based on biochemical processes programmed by appropriate genetic information. Endospore formation occurs in prokaryotes and fungi.

The endospore is formed inside the mother cell (sporangium), has specific structures: multilayer protein covers, outer and inner membranes, cortex (Fig. 7.). Endospores are resistant to elevated temperatures and radiation doses, which are similar for vegetative cells. Spore-forming bacteria include a large number of prokaryotes from 15 genera, including rod-shaped, spherical, spirillum and filamentous organisms. All of them have a cell wall characteristic of gram-positive prokaryotes. As a rule, one endospore is formed in each bacterial cell.

The process of sporulation has been best studied in representatives of the genera Bacillus and Clostridium. Before sporulation, the DNA of the vegetative cell divides. A strand is formed along the long axis of the cell, then approximately 1/3 of the strand separates and passes into the forming spore at one of the poles of the cell. Then the cytoplasm is compacted, which, together with DNA, is separated from the rest of the cell contents using a septum. The septum is formed by invagination of the CPM from the periphery to the center, where it fuses and the spore membrane is formed. The cut off area is “overgrown” with a second membrane and a prospore is formed. At the next stage, a cortex begins to form between the prospore membranes, and spore integument, consisting of several layers, is synthesized on the outside.

Rice. 4 a and b - formation of the septum, c and d - surrounding the spore protoplast by the protoplast of the mother cell, e formation of the cortex and spore membranes; f - diagram of the structure of a mature spore: 1 - exosporium, 2 - outer shell of the spore; 3 - inner shell of the spore, 4 - cortex; 5 - cell wall of the embryo, 6 - cytoplasmic membrane, 7 - cytoplasm with nuclear substance

In many bacteria, another structure is formed on top of the endospore covers - the exosporium, the structure of which depends on the type of bacteria. In prokaryotes from the genus Clostridium, appendages on the exosporium of various structures, sometimes very bizarre, were found (Fig. 8). The functional significance of these outgrowths is not clear.

Endospores of prokaryotes are characterized by a very low level of metabolism; they are very resistant to environmental factors: high and low temperatures, dehydration, lytic factors, high acidity of the environment, radiation, mechanical stress, etc. The mechanisms of endospore resistance have not yet been well studied. It is believed that prokaryotic endospores are stabilized by the dehydrated state of the cytoplasm, the heat resistance of spore enzymes, the presence of dipicolinic acid and a large number of divalent cations. The stability of endospores is also facilitated by surface structures: membranes, cortex, integument, which mechanically protect the contents of the endospore from penetration of aggressive substances from the outside.

Formed resting endospores can remain in a viable state for varying periods of time: from several days to 1000 years or more. Below is the dependence of the survival of spores of different groups of bacteria on damaging factors (high temperature and drying).

Table 1

On microscopic examination, endospores are clearly visible. In doubtful cases, you can use special staining, for which the fixed preparation must be boiled with a fuchsin carbolic solution. Endospores firmly bind the dye and do not discolor even when treated with ethanol or acetic acid; all other contents of the cell become discolored.

The endospore contains almost all the dry matter of the cell, but occupies 10 times less volume. Endospores are not an obligatory stage of the bacilli life cycle. Under favorable nutritional conditions, bacilli can multiply by division indefinitely. The formation of endospores begins only when there is a lack of nutrients and when metabolic products accumulate in excess.

Under favorable conditions, most endospores germinate. The percentage of endospore germination can be increased by heating some spores in water at 60 °C for 5 minutes, others at 100 °C for 10 minutes. Heat shock should be carried out immediately before sowing.

In the food industry, to destroy heat-resistant endospores of bacteria, they resort to expensive sterilization of food products. For example, if during pasteurization (heating at 80 °C for 10 minutes) of food products, the vegetative cells of spore-forming bacteria and all other bacteria die, then heat-resistant endospores can withstand much stronger heating, and some spores can even withstand boiling for several hours.

Classification of bacteria

As more and more new bacteria were described, an urgent need arose to systematize and compare the newly described cultures with known ones. At the end of the 19th - beginning of the 20th centuries. Determinants of bacteria have appeared that help classify and identify newly isolated bacteria according to certain characteristics. In classification, the main task is to determine the type of bacteria.

A species is a group of closely related organisms that have the same origin and are characterized by certain morphological, biochemical and physiological characteristics that contribute to adaptation to a specific habitat.

Species are united into genera, genera into families, then orders, classes, divisions, and kingdoms follow. The type of bacteria is described using characteristics: morphological, cultural, physiological-biochemical, etc.

Morphological characteristics are cell shape, presence or absence of flagella, capsules, ability to sporulate, and Gram staining.

Cultural characteristics include the general appearance of the bacterial colony, the presence of pigment, etc.

Physiological and biochemical characteristics are the method of obtaining energy, the need for nutrients, attitude to environmental factors, etc.

The most modern determinant for identifying bacteria is “Bergie's Brief Determinant of Bacteria,” which most fully describes known bacteria. In the 8th edition of this key, all bacteria, with the exception of cyanobacteria, are grouped into 19 parts. Below is a brief description of them:

Part 1. Phototrophic bacteria. This part contains grouped photosynthetic bacteria, characterized by a specific set of pigments and a special type of photosynthesis: purple bacteria and green sulfur bacteria. The pigments are represented by various types of bacteriochlorophyll and carotenoids. Photosynthesis is not accompanied by the release of oxygen. These are predominantly aquatic microorganisms.

Part 2. Sliding bacteria. The composition of bacteria in this part includes two orders: myxobacteria (Mixobacteriales) and cytophages (Cytoppagales). The first order includes bacteria that form a layer of mucus around the cell. Bacteria are mobile. Myxobacteria form so-called fruiting bodies, within which the cells enter a dormant state. The second order includes bacteria that are similar in type of movement to myxobacteria, but do not form fruiting bodies. The order includes four families of predominantly aquatic bacteria.

Part 3. Chlamydobacteria. This part consists of filamentous bacteria surrounded by a common vagina and mucous membrane. The vagina consists of a heteropolysaccharide, often encrusted with oxides of iron or manganese. Found in water bodies and soil.

Part 4. Budding and (or) stem bacteria. This part includes bacteria that form appendages (stalks), consisting of mucus and cells not associated with the cytoplasm, as well as bacteria that form filamentous cellular outgrowths - prosteks. Bacteria are widespread in soil and water bodies.

Part 5. Spirochetes. This part brings together bacteria that have the appearance of thin spiral-shaped single-celled forms. Many bacteria are pathogenic, causing syphilis and relapsing fever.

Part 7. Gram-negative aerobic rods and cocci. This part of the bacteria includes five families, one of which - Pseudomonas - is widely distributed in nature: in the air, soil, sea and fresh waters, sludge, sewage, and food products. In the latter, bacteria of this family cause spoilage.

Part 8. Gram-negative facultative anaerobic rods. This part includes two families: Enterobacteriaceae and Vibrionaceae. Enterobacteriacea is a Gram-negative, sporeless, aerobic or facultative anaerobic bacilli. The most studied representatives of this family are the bacteria Escherichia coli, which are always found in the intestines of humans and animals, therefore the contamination of water and food products is judged by the presence of E. coli in them. E. coli are among the opportunistic bacteria. Bacteria of this family from the genera Salmonella and Shigella are among the causative agents of severe intestinal diseases in humans. The bacteria Salmonella typhi are the causative agents of typhoid fever. Bacteria of the genus Shigella are the causative agents of bacterial dysentery. The Vibrionaceae family includes bacteria of the species Vibrio cholerae, the causative agent of Asian cholera.

Part 9. Gram-negative anaerobic bacteria. The bacteria grouped in this part belong to the Bacteroidaceae family. They are all sticks; These are obligate anaerobes. The main habitat of these bacteria is the intestines of humans and animals, and the digestive tract of insects. Some species are pathogenic and cause various lesions of the skin, a number of organs and tissues of the body.

Part 13. Methane-producing bacteria. This part is represented by one family - Methanobacteriaceae. All bacteria are homogeneous in physiological characteristics: they are obligate anaerobes; the main product of energy metabolism is methane. The main habitats are swamps, various treatment facilities, and the rumen of ruminants.

Part 14. Gram-positive cocci. This part includes two groups. The first group is aerobic and (or) facultative anaerobic bacteria of the Micrococcaceae and Streptococcaceae families. The second group is obligate anaerobes of the Peptococcaceae family. Bacteria of the family Micrococcaceae are cocci that divide in more than one plane, sometimes do not diverge, forming clusters of spherical or irregular shape. Energy is obtained through respiration or fermentation. These are mainly saprophytes that destroy many complex organic substances and act as “scavengers.” Many of them are causative agents of food spoilage. Among them there are pathogenic forms belonging to the genus Staphylococcus. Developing on food products, they produce toxins that cause poisoning.

Bacteria of the family Streptococcaceae are cocci, nonmotile, nonsporeless, facultative anaerobic. Bacteria of the genera Streptococcus, Pediococcus, Aerococcus are homofermentative lactic acid; bacteria of the genus Leuconostoc are heterofermentative lactic acid bacteria.

Bacteria of the Peptococcaceae family are obligate anaerobic cocci that live in the soil, on the surface of cereals, in the oral cavity, gastrointestinal tract, and respiratory tract of humans and animals; some species are pathogenic.

Part 15. Rods and cocci forming endospores. This part is represented by one family - Bacillaceae, which includes five genera. Two of them - bacilli (Bacillus) and clostridia (Clostridium) - are the most numerous and are of the greatest interest. Bacilli are rod-shaped bacteria; most of them are mobile; form endospores; obligate or facultative aerobes. Bacilli synthesize various lytic enzymes that break down proteins, fats, polysaccharides and other macromolecules. Some species produce antibiotics. Most are saprophytes. The main habitat is soil. Many bacilli are causative agents of food spoilage. Among them there are species pathogenic for humans and animals, for example Bacillus anthracis, the causative agent of anthrax.

The genus Clostridium includes rods that differ from bacilli in the form of sporulation and obligate anaerobic mode of existence. They cause butyric acid fermentation, most clostridia are saprophytes, inhabitants of the soil. Some species live in the intestines of humans and animals, for example Cl. teteni -- the causative agent of tetanus, Cl. perfringens is the causative agent of gas gangrene, CL botulinum is a producer of exotoxin, one of the most powerful biological poisons.

Part 16. Gram-positive asporogenous rod-shaped bacteria. This part is also represented by one family - Lactobacillaceae, which includes one genus - Lactobacillus. Bacteria obtain energy through homofermentative or heterofermentative lactic acid fermentation and are widely distributed in nature: in soil, on decomposing animal and plant remains, in the intestines of vertebrates, in milk, and dairy products. There are pathogenic forms. Many bacteria are used in the production of fermented milk products, cheeses, pickling vegetables, dough, etc.

Part 17. Actinomycetes and related organisms. This part combines corynebacteria, propionic acid bacteria and actipomycetes.

Of the existing species of propionic acid bacteria, the species of greatest interest in the microbiology of food products is the species Propionibacterium freudenreichii of the genus Propionibacterium. Bacteria of this genus are gram-positive, non-motile rods that do not form spores. These are obligate anaerobes. Propionic acid bacteria are widely used in cheese production.

Actinomycetes include bacteria that form branching threads and sometimes developed mycelium. They have different methods of reproduction. Most actinomycetes reproduce using spores produced on sporangia, which can be long or short, straight or spiral-shaped with a different number of curls and location. Actinomycetes are represented by two families: Mycobacteriaceae and Streptomycetaccae. The Mycobacteriaceae family is represented by one genus - Mycobacterium, a characteristic feature of which is the formation of branching forms at a young age.

Most mycobacteria are saprophytes, live in the soil and use a wide variety of organic compounds: proteins, carbohydrates, fats, waxes, paraffins. Some species are pathogenic, for example M. tuberculosis - the causative agent of tuberculosis, M. leprae - the causative agent of leprosy.

Representatives of the Streptomycetaceae family form well-developed aerial mycelium and reproduce by spores formed at the ends of hyphae and pieces of mycelium. There are about 500 species. Many streptomycetes synthesize antibiotics that are active against bacteria, fungi, algae, protozoa, phages and have an antitumor effect.

Part 18. Rickettsia. This part includes two orders of bacteria - rickettsia (Rickettsiales) and chlamydia (Chlamydiales).

Rickettsiae are nonmotile bacteria that reproduce gram-negatively only in host cells, causing rickettsiosis. There are non-pathogenic species.

Part 19. Mycoplasmas. Mycoplasmas are prokaryotes that lack a cell wall and are limited by a single three-layer membrane. The cells are very small, sometimes ultramicroscopic, pleomorphic. The method of reproduction is not entirely clear; Apparently, it occurs due to the formation of coccoid structures of “elementary bodies”; bipair division and reproduction by budding are possible. The resting stages are unknown. In terms of the amount of genetic information contained in the genome, mycoplasmas occupy an intermediate position between E. coli and T-phages.

Systematics and morphology of microorganisms

1. Taxonomy of microorganisms

Taxonomy is the distribution of microorganisms according to their origin and biological similarity. Systematics deals with a comprehensive description of species of organisms, elucidation of the degree of related relationships between them and their unification into classification units of different levels of relatedness - taxa. The main issues addressed in taxonomy (three aspects, three pillars of taxonomy) are classification, identification and nomenclature.

Classification is the distribution (association) of organisms in accordance with their general properties (similar genotypic and phenotypic characteristics) into various taxa.

Taxonomy is the science of methods and principles of distribution (classification) of organisms in accordance with their hierarchy. The most commonly used taxonomic units (taxa) are strain, species, genus. Subsequent larger taxa - family, order, class.

In modern terms species in microbiology- a set of microorganisms that have a common evolutionary origin, a close genotype (a high degree of genetic homology, usually more than 60%) and the closest possible phenotypic characteristics.

Numerical (numerical) taxonomy is based on the use of the maximum number of comparable characteristics and mathematical consideration of the degree of correspondence. The large number of compared phenotypic characteristics and the principle of their equal importance made classification difficult.

When studying, identifying and classifying microorganisms, the following (geno- and phenotypic) characteristics are most often studied:

1. Morphological - shape, size, features of relative position, structure.

2. Tinctorial - relation to various dyes (nature of staining), primarily to Gram staining. On this basis, all microorganisms are divided into gram-positive and gram-negative.

Morphological properties and relation to Gram staining make it possible, as a rule, to classify the microorganism under study as belonging to large taxa - family, genus.

3. Cultural - the nature of the growth of the microorganism on nutrient media.

4. Biochemical - the ability to ferment various substrates(carbohydrates, proteins and amino acids, etc.), form various biochemical products in the process of life due to the activity of various enzyme systems and metabolic characteristics.

5. Antigenic - depend mainly on the chemical composition and structure of the cell wall, the presence of flagella, capsules, are recognized by the ability of the macroorganism (host) to produce antibodies and other forms of immune response, are detected in immunological reactions.

6. Physiological - methods of carbohydrate (autotrophs, heterotrophs), nitrogen (aminoautotrophs, aminoheterotrophs) and other types of nutrition, type of respiration (aerobes, microaerophiles, facultative anaerobes, strict anaerobes).

7. Mobility and types of movement.

8. Ability to form spores, nature of spores.

9. Sensitivity to bacteriophages, phage typing.

10. Chemical composition of cell walls - basic sugars and amino acids, lipid and fatty acid composition.

11. Protein spectrum (polypeptide profile).

12. Sensitivity to antibiotics and other drugs.

13. Genotypic (use of genosystematic methods).

In recent decades, to classify microorganisms, in addition to their phenotypic characteristics (see paragraphs 1 - 12), various genetic methods (study of genotype - genotypic properties). More and more advanced methods are used - restriction analysis, DNA - DNA hybridization, PCR, sequencing, etc. Most methods are based on the principle of determining the degree of homology of genetic material (DNA, RNA). In this case, they often proceed from the conditional assumption that the degree of homology of more than 60% (for some groups of microorganisms - 80%) indicates that the microorganisms belong to the same species (different genotypes - one genotype), 40-60% - to the same genus.

Identification.

The basic phenotypic and genotypic characteristics used to classify microorganisms are also used for identification, i.e. establishing their taxonomic position and, above all, species, is the most important aspect of the microbiological diagnosis of infectious diseases. Identification is carried out on the basis of studying the pheno- and genotypic characteristics of the infectious agent being studied and comparing them with the characteristics of known species. In this work, reference strains of microorganisms, standard antigens, and immune sera are often used against known prototype microorganisms. In pathogenic microorganisms, morphological, tinctorial, cultural, biochemical and antigenic properties are often studied.

Nomenclature - the name of microorganisms in accordance with international rules. To designate bacterial species, the binary Latin nomenclature genus/species is used, consisting of the name of the genus (written with a capital letter) and the species (written with a lowercase letter). Examples: Shigella flexneri, Rickettsia sibirica.

In microbiology, a number of other terms are often used to characterize microorganisms.

Strain - any specific sample (isolate) of a given species. Strains of the same species, differing in antigenic characteristics, are called serotypes (serovariants, abbreviated as serovars), in terms of sensitivity to specific phages - phagotypes, in biochemical properties - chemovars, in biological properties - biovars, etc.

A colony is a visible isolated structure when bacteria multiply on solid nutrient media; it can develop from one or more parent cells. If a colony develops from one parent cell, then the offspring is called a clone.

Culture is the entire collection of microorganisms of the same species grown on a solid or liquid nutrient medium.

The basic principle of bacteriological work is isolating and studying the properties of only pure(homogeneous, without admixture of foreign microflora) crops.

2. Morphology of bacteria

Prokaryotes differ from eukaryotes in a number of basic characteristics.

1. Lack of a true differentiated nucleus (nuclear membrane).

2. Lack of developed endoplasmic reticulum and Golgi apparatus.

3. Absence of mitochondria, chloroplasts, lysosomes.

4. Inability to endocytosis (capture food particles).

5. Cell division is not associated with cyclic changes in cell structure.

6. Significantly smaller sizes (usually). Most bacteria are 0.5-0.8 micrometers (µm) x 2-3 µm in size.

Based on their shape, the following main groups of microorganisms are distinguished.

1. Globular or cocci (from Greek - grain).

2. Rod-shaped.

3.Crimped.

4. Thread-like.

Coccoid bacteria (cocci) by the nature of the relationship after division they are divided into a number of options.

1. Micrococci. The cells are located alone. They are part of the normal microflora and are found in the external environment. They do not cause diseases in humans.

2. Diplococci. The division of these microorganisms occurs in one plane, pairs of cells are formed. Among diplococci there are many pathogenic microorganisms - gonococcus, meningococcus, pneumococcus.

3. Streptococci. Division is carried out in one plane, the multiplying cells maintain connection (do not diverge), forming chains. There are many pathogenic microorganisms that cause sore throats, scarlet fever, and purulent inflammatory processes.

4. Tetracocci. Division in two mutually perpendicular planes with the formation of tetrads (i.e. four cells). They have no medical significance.

5. Sarcins. Division in three mutually perpendicular planes, forming bales (packages) of 8, 16 or more cells. Often found in the air.

6. Staphylococci (from Latin - bunch of grapes). They divide randomly in different planes, forming clusters resembling bunches of grapes. They cause numerous diseases, primarily purulent-inflammatory ones.

Rod-shaped microorganisms.

1. Bacteria are rods that do not form spores.

2. Bacilli are aerobic spore-forming microbes. The diameter of the spore usually does not exceed the size (“width”) of the cell (endospore).

3. Clostridia are anaerobic spore-forming microbes. The diameter of the spore is larger than the diameter (diameter) of the vegetative cell, causing the cell to resemble a spindle or tennis racket.

It must be kept in mind that the term “bacteria” is often used to refer to all prokaryotic microbes. In a narrower (morphological) sense, bacteria are rod-shaped forms of prokaryotes that do not have spores.

Twisted forms of microorganisms.

1. Vibrios and campylobacters - have one bend, can be in the shape of a comma, a short curl.

2.Spirillas - have 2-3 curls.

3. Spirochetes - have a different number of whorls, axostyle - a set of fibrils, a specific pattern of movement and structural features (especially the terminal sections) for different representatives. Of the large number of spirochetes, representatives of three genera are of greatest medical importance - Borrelia, Treponema, Leptospira.

Characteristics of the morphology of rickettsia, chlamydia, mycoplasmas, more detailed characteristics of vibrios and spirochetes will be given in the relevant sections of private microbiology.

We conclude this section with a brief description (key) for characterizing the main genera of microorganisms of medical importance, based on the criteria used in the Bergey identification of bacteria.

Table. Key to the main groups of bacteria

Main groups of bacteria - Genera of bacteria

1. Curving bacteria with thin walls, mobility is ensured by sliding - gliding bacteria

Treponema

2. Curving bacteria with thin walls, mobility is associated with the presence of an axial thread - spirochetes

Borrelia, Leptospira

A. Mycelial forms

Mycobacterium, Actinomyces, Nocardia, Streptomyces

B. Simple unicellular

Rickettsia, Coxiella, Chlamydia

2/free living

A. gram-positive:

cocci - Streptococcus, Staphylococcus

non-spore-forming rods

Corynebacterium, Listeria, Erysipelothrix

spore-forming rods

incl. obligate aerobes - Bacillus

incl. obligate anaerobes - Clostridium

b. gram negative:

cocci - Neisseria

non-coliform bacteria

incl. spiral shape - Spirillum

incl. straight, very small sticks

Pasteurella, Brucella, Yersinia, Francisella, Haemophilus, Bordetella

coli

incl. facultative anaerobes

Escherichia, Salmonella, Shigella, Klebsiella, Proteus, Vibrio

incl. obligate aerobes - Pseudomonas

incl. obligate anaerobes - Bacteroides, Fusobacterium

4.Without cell walls - Mycoplasma, Ureaplasma

3. Structure of a bacterial cell

The obligatory organelles are: nuclear apparatus, cytoplasm, cytoplasmic membrane.

Optional(minor) structural elements are: cell wall, capsule, spores, pili, flagella.

1. In the center of the bacterial cell there is a nucleoid - a nuclear formation, most often represented by one ring-shaped chromosome. Consists of a double-stranded DNA strand. The nucleoid is not separated from the cytoplasm by the nuclear membrane.

2. Cytoplasm is a complex colloidal system containing various inclusions of metabolic origin (grains of volutin, glycogen, granulosa, etc.), ribosomes and other elements of the protein synthesizing system, plasmids (extranucleoid DNA), mesosomes(formed as a result of invagination of the cytoplasmic membrane into the cytoplasm, participate in energy metabolism, sporulation, and the formation of the intercellular septum during division).

3. The cytoplasmic membrane limits the cytoplasm on the outer side, has a three-layer structure and performs a number of important functions - barrier (creates and maintains osmotic pressure), energy (contains many enzyme systems - respiratory, redox, carries out electron transfer), transport (transfer of various substances into and out of the cell).

4. Cell wall - inherent in most bacteria (except for mycoplasmas, acholeplasmas and some other microorganisms that do not have a true cell wall). It has a number of functions, primarily providing mechanical protection and a constant shape of cells; the antigenic properties of bacteria are largely associated with its presence. It consists of two main layers, of which the outer one is more plastic, the inner one is rigid.

The main chemical compound of the cell wall, which is specific only to bacteria - peptidoglycan(mureic acids). An important characteristic for taxonomy of bacteria depends on the structure and chemical composition of the bacterial cell wall - Relation to Gram stain. In accordance with it, two large groups are distinguished: gram-positive (“gram +”) and gram-negative (“gram -”) bacteria. The wall of gram-positive bacteria after Gram staining retains the iodine complex with gentian violet(colored blue-violet), gram-negative bacteria lose this complex and the corresponding color after treatment and are colored pink due to staining with fuchsin.

Features of the cell wall of gram-positive bacteria.

A powerful, thick, simply organized cell wall, which is dominated by peptidoglycan and teichoic acids, no lipopolysaccharides (LPS), and often no diaminopimelic acid.

Features of the cell wall of gram-negative bacteria.

The cell wall is much thinner than that of gram-positive bacteria and contains LPS, lipoproteins, phospholipids, and diaminopimelic acid. The structure is more complex - there is an outer membrane, so the cell wall is three-layered.

When Gram-positive bacteria are treated with enzymes that destroy peptidoglycan, structures called protoplasts appear that are completely devoid of a cell wall. Treatment of gram-negative bacteria with lysozyme destroys only the peptidoglycan layer, without completely destroying the outer membrane; such structures are called spheroplasts. Protoplasts and spheroplasts have a spherical shape (this property is associated with osmotic pressure and is characteristic of all cell-free forms of bacteria).

L- forms of bacteria.

Under the influence of a number of factors that adversely affect the bacterial cell (antibiotics, enzymes, antibodies, etc.), L- transformation bacteria, leading to permanent or temporary loss of the cell wall. L-transformation is not only a form of variability, but also an adaptation of bacteria to unfavorable living conditions. As a result of changes in antigenic properties (loss of O- and K-antigens), a decrease in virulence and other factors, L-forms acquire the ability to remain for a long time ( persist) in the host’s body, maintaining a sluggish infectious process. The loss of the cell wall makes L-forms insensitive to antibiotics, antibodies and various chemotherapy drugs, the point of application of which is the bacterial cell wall. Unstable L-forms are capable reverse into classical (original) forms of bacteria that have a cell wall. There are also stable L-forms of bacteria, the absence of a cell wall and the inability to reverse into the classical forms of bacteria are genetically fixed. In a number of ways, they are very similar to mycoplasmas and other Mollicutes- bacteria that lack a cell wall as a taxonomic feature. Microorganisms belonging to mycoplasmas are the smallest prokaryotes, do not have a cell wall and, like all bacterial wallless structures, have a spherical shape.

To the surface structures of bacteria(optional, like the cell wall), include capsule, flagella, microvilli.

Capsule or a mucous layer surrounds the membrane of a number of bacteria. Highlight microcapsule, detected by electron microscopy in the form of a layer of microfibrils, and macrocapsule, detectable by light microscopy. The capsule is a protective structure (primarily from drying out); in a number of microbes it is a pathogenicity factor, prevents phagocytosis, and inhibits the first stages of protective reactions—recognition and absorption. U saprophytes capsules are formed in the external environment, in pathogens, more often in the host body. There are a number of methods for coloring capsules depending on their chemical composition. The capsule often consists of polysaccharides (the most common color is Ginsu), less often from polypeptides.

Flagella. Motile bacteria can be gliding (move along a solid surface as a result of wave-like contractions) or floating, moving due to filament-like spirally curved proteins ( flagellinaceae by chemical composition) formations - flagella.

Based on the location and number of flagella, a number of forms of bacteria are distinguished.

1.Monotrichous - have one polar flagellum.

2. Lophotrichs - have a polarly located bundle of flagella.

3.Amphitrichous - have flagella at diametrically opposite poles.

4. Peritrichous - have flagella along the entire perimeter of the bacterial cell.

The ability for purposeful movement (chemotaxis, aerotaxis, phototaxis) in bacteria is genetically determined.

Fimbriae or cilia- short filaments, in large numbers surrounding the bacterial cell, with the help of which bacteria are attached to substrates (for example, to the surface of mucous membranes). Thus, fimbriae are factors of adhesion and colonization.

F- pili (fertility factor)- apparatus bacterial conjugation, are found in small quantities in the form of thin protein fibers.

Endospores and sporulation.

Sporulation- a method of preserving certain types of bacteria in unfavorable environmental conditions. Endospores are formed in the cytoplasm, are cells with low metabolic activity and high resistance ( resistance) to drying, chemical factors, high temperature and other unfavorable environmental factors. Light microscopy is often used to identify spores. according to Ozheshko. High resistance is associated with high content calcium salt of dipicolinic acid spores in the shell. The location and size of spores in different microorganisms differs, which has differential diagnostic (taxonomic) significance. The main phases of the “life cycle” of spores sporulation(includes preparatory stage, prespore stage, shell formation, maturation and dormancy) and germination, ending with the formation of a vegetative form. The process of sporulation is genetically determined.

Unculturable forms of bacteria.

Many species of gram-negative bacteria that do not form spores have a special adaptive state - uncultivable forms. They have low metabolic activity and do not actively reproduce, i.e. They do not form colonies on solid nutrient media and are not detected by culture. They are highly resistant and can remain viable for several years. Not detected by classical bacteriological methods, detected only using genetic methods ( polymerase chain reaction - PCR).

4. Morphological characteristics of mushrooms

Fungi and protozoa have a clearly defined nucleus and are classified as eukaryotes. Fungi are larger than bacteria, in evolutionary terms they are close to plants (the presence of a cell wall containing chitin or cellulose, vacuoles with cell sap, inability to move, visible movement of the cytoplasm). The nuclear material of fungi is separated from the cytoplasm by the nuclear membrane. Yeast fungi form individual oval cells. Mold fungi form cellular thread-like structures called hyphae. Mycelium - interweaving of hyphae - the main morphological structure. In lower fungi, the mycelium is unicellular and has no internal partitions ( sept). Fungi reproduce sexually and asexually (vegetatively). During vegetative propagation, specialized reproductive structures are formed - spores - conidia. They can be located in specialized containers - sporangia(endospores) or detach from fruiting hyphae (exospores). Less commonly observed is the formation of spores inside cells ( oidii), which are segments of hyphae. Yeast cells reproduce by budding and do not form mycelium. Sexual reproduction involves the interaction of specialized cells that have significant differences in morphology in different fungi and are often used as a differential diagnostic feature.

Most species of fungi of medical importance are characterized by the presence of conidia (or exospores), which are forms of nonsexual reproduction. Their classification is largely based on the morphological forms of conidia. Their most common forms are blastopores, chlamydospores, arthrospores, conidiospores.

Blastospores are simple structures that are formed as a result of budding, followed by separation of the bud from the parent cell, for example in yeast fungi.

Chlamydospores are formed as a result of the enlargement of hyphal cells to form a thick membrane that protects the spores from unfavorable environmental conditions.

Arthrospores are spores formed by fragmentation of hyphae into individual cells. They are found in yeast-like fungi, the causative agent of coccidioidosis, tissue forms of dermatophytes in hair, skin scales and nails.

Conidiospores are mature external spores that arise on differentiated conidiophores (conidiophores), differing from other mycelial threads in shape and size (in Aspergillus, penicillium) or located on the sides and ends of any branch of the mycelium, attaching to it directly or with a thin stalk.

Endospores of perfect fungi include sporangiospores of mucor fungi, developing in special organs (sporangia) located at the top of the sporangiophore. The spores are released when the wall of the sporangium ruptures.

Endospores are also found in tissue forms of coccidioidosis pathogens. They develop in round formations - spherules; when the wall of a mature spherule ruptures, they enter the external environment.

The main functional difference between spores in bacteria and fungi: in bacteria, spores provide survival in unfavorable environmental conditions, in fungi, the formation of spores is a method of reproduction.

5. Morphological characteristics of actinomycetes (radiant fungi according to old classifications)

Actinomycetes are forms of bacteria that have true mycelium without partitions. The mycelial (in the form of branching threads) growth of these gram-positive bacteria gives them an external resemblance to fungi. This similarity is enhanced by the presence in higher forms of actinomycetes of external non-sexual spores, which are called conidia.

Unlike fungi, actinomycetes have a prokaryotic cell structure, do not contain chitin or cellulose in the cell wall, and reproduce only asexually. In lower actinomycetes, the mycelium is fragmented into typical unicellular bacteria. The mycelium of actinomycetes is divided into substrate (in the substrate) and aerial. Filamentous bacteria include mycobacteria, the genera Nacardia and actinomycetes, and several genera of higher actinomycetes.

Representatives of the genus Mycobacterium, which includes the causative agents of tuberculosis, are acid-fast microorganisms that do not accept paint well. Their high resistance in the external environment, acid resistance and a number of other properties are associated with the special composition of the cell wall, high content of lipids and wax.

Microorganisms belonging to higher actinomycetes (genus Streptomyces, Micromonospora) form mycelium and reproduce by external non-sexual spores or conidia. The usual habitat for most of them is soil. However, a number of actinomycetes and nocardia species can infect wounds and cause abscess formation. Actinomycetes are characterized by the formation of drusen - dense “grains” in the pus, which are randomly intertwined filaments of mycelium in the center with radial “clubs” extending to the periphery, flask-shaped, widened at the ends. Some actinomycetes (such as streptomycetes) are associated with the ability to produce antibiotics.

6. Morphological characteristics of protozoa

Literature:

2. Koralyuk A.M. "Medical Microbiology", 2002.

3. Deryabin D.G. "Staphylococci: ecology and pathogenicity", 2000.

4. Identifier of bacteria Bergey, in 2 volumes.

5. Shub G.M., Korzhenevich V.I. "Short course in medical microbiology", 2001.

Microorganisms.

The shape and size of microorganisms are very diverse.

Based on their shape, the following main groups of microorganisms are distinguished.

1. Globular or cocci (from Greek - grain).

2. Rod-shaped.

3.Crimped.

Coccoid bacteria (cocci) by the nature of the relationship after division they are divided into a number of options.

1.Micrococci. The cells are located alone. They are part of the normal microflora and are found in the external environment. They do not cause diseases in humans.

2.Diplococci. The division of these microorganisms occurs in one plane, pairs of cells are formed. Among diplococci there are many pathogenic microorganisms - gonococcus, meningococcus, pneumococcus.

3.Streptococci. Division is carried out in one plane, the multiplying cells maintain connection (do not diverge), forming chains. There are many pathogenic microorganisms - causative agents of sore throats, scarlet fever, and purulent inflammatory processes.

4.Tetracocci. Division in two mutually perpendicular planes with the formation of tetrads (i.e., four cells). They have no medical significance.

5.Sarcins. Division in three mutually perpendicular planes, forming bales (packages) of 8, 16 or more cells. Often found in the air.

6.Staphylococcus(from Latin - bunch of grapes). They divide randomly in different planes, forming clusters resembling bunches of grapes. They cause numerous diseases, primarily purulent-inflammatory ones.

Rod-shaped microorganisms.

1. Bacteria are rods that do not form spores.

2.Bacilli are aerobic spore-forming microbes. The diameter of the spore usually does not exceed the size (“width”) of the cell (endospore).

3. Clostridia are anaerobic spore-forming microbes. The diameter of the spore is larger than the diameter (diameter) of the vegetative cell, causing the cell to resemble a spindle or tennis racket.

It must be kept in mind that the term “bacterium” is often used to refer to all prokaryotic microbes. In a narrower (morphological) sense, bacteria are rod-shaped forms of prokaryotes that do not have spores.

Twisted forms of microorganisms.

1.Spirillas - have 2-3 curls.

2. Spirochetes - have a different number of whorls, axostyle - a set of fibrils, a specific pattern of movement and structural features (especially the terminal sections) for different representatives. Of the large number of spirochetes, representatives of three genera are of greatest medical importance - Borrelia, Treponema, Leptospira.

The structure of a bacterial cell.

The obligatory organelles are: nucleoid, cytoplasm, cytoplasmic membrane.

Optional(minor) structural elements are: inclusions, capsule, spores, pili, flagella.

1.In the center of the bacterial cell is nucleoid- a nuclear formation, most often represented by one ring-shaped chromosome. Consists of a double-stranded DNA strand. The nucleoid is not separated from the cytoplasm by the nuclear membrane.

Basic properties of viruses, in which they differ from the rest of the living world.

1.Ultramicroscopic dimensions (measured in nanometers). Large viruses (smallpox virus) can reach sizes of 300 nm, small ones - from 20 to 40 nm. 1mm=1000µm, 1µm=1000nm.

3.Viruses are not capable of growth and binary fission.

4.Viruses reproduce by reproducing themselves in an infected host cell using their own genomic nucleic acid.

6.The habitat of viruses is living cells - bacteria (these are bacterial viruses or bacteriophages), plant, animal and human cells.

All viruses exist in two qualitatively different forms: extracellular - virion and intracellular - virus. The taxonomy of these representatives of the microcosm is based on the characteristics of virions - the final phase of virus development.

Structure (morphology) of viruses.

1.Virus genome form nucleic acids, represented by single-stranded RNA molecules (in most RNA viruses) or double-stranded DNA molecules (in most DNA viruses).

2.Capsid- a protein shell in which the genomic nucleic acid is packaged. The capsid consists of identical protein subunits - capsomers. There are two ways of packing capsomers into a capsid - helical (helical viruses) and cubic (spherical viruses).

With spiral symmetry protein subunits are arranged in a spiral, and between them, also in a spiral, the genomic nucleic acid (filamentous viruses) is laid out. With cubic type of symmetry virions can be in the form of polyhedra, most often - twenty-hedra - Icosahedrons.

3.Simply designed viruses only have nucleocapsid, i.e., the genome complex with the capsid is called “naked.”

4. Other viruses have an additional membrane-like shell on top of the capsid, acquired by the virus at the time of exit from the host cell - supercapsid. Such viruses are called “dressed”.

In addition to viruses, there are even more simply organized forms of agents capable of being transmitted - plasmids, viroids and prions.

Morphology of Rickettsia

Rickettsia does not have spores, capsules, and is immobile. Gram negative. According to Romanovsky-Giemsa and according to the Zdrodovsky method, they are painted red. The structure of the cell wall is similar to the structure of the wall of gram-negative bacteria.

They are causative agents of typhus and Bril's disease.

Morphological characteristics of fungi.

Fungi and protozoa have a clearly defined nucleus and are classified as eukaryotes. Fungi are larger than bacteria, in evolutionary terms they are close to plants (the presence of a cell wall containing chitin or cellulose, vacuoles with cell sap, inability to move, visible movement of the cytoplasm). The nuclear material of fungi is separated from the cytoplasm by the nuclear membrane. Yeast fungi form individual oval cells. Mold fungi form cellular filament-like structures - hyphae. Mycelium- interweaving of hyphae - the main morphological structure. In lower fungi, the mycelium is unicellular and has no internal partitions ( sept). Fungi reproduce sexually and asexually (vegetatively). During vegetative propagation, specialized reproductive structures are formed - spores - conidia. They can be located in specialized containers - sporangia(endospores) or detach from fruiting hyphae (exospores).

Conidiospores are mature external spores that arise on differentiated conidiophores (conidiophores), differing from other mycelial threads in shape and size (in Aspergillus, penicillium) or located on the sides and ends of any branch of the mycelium, attaching to it directly or with a thin stalk.

Endospores of perfect fungi include sporangiospores of mucor fungi, developing in special organs (sporangia) located at the top of the sporangiophore. The spores are released when the wall of the sporangium ruptures.

The main functional difference between spores in bacteria and fungi: in bacteria, spores provide survival in unfavorable environmental conditions, in fungi, the formation of spores is a method of reproduction.

Morphological characteristics of actinomycetes(radiant mushrooms according to old classifications). Actinomycetes are forms of bacteria that have true mycelium without partitions. The mycelial (in the form of branching threads) growth of these gram-positive bacteria gives them an external resemblance to fungi. This similarity is enhanced by the presence in higher forms of actinomycetes of external non-sexual spores, which are called conidia.

Unlike fungi, actinomycetes have a prokaryotic cell structure, do not contain chitin or cellulose in the cell wall, and reproduce only asexually. In lower actinomycetes, the mycelium is fragmented into typical unicellular bacteria.

The usual habitat for most of them is soil. However, a number of actinomycete species can infect wounds and cause abscess formation. Some actinomycetes (such as streptomycetes) are associated with the ability to produce antibiotics.

The student must know: the morphology of bacteria, methods of microscopic examination, rules for staining bacteria.

Key words and terms: nucleoid. Capsule. Spore. Flagella. Cytoplasmic membrane. Cell wall.

MORPHOLOGY OF BACTERIA

Bacteria can be round, rod-shaped or convoluted. Round bacteria are called cocci (one cell is a coccus). The word "kokk" comes from the Greek word "kokkos", which means seed. Usually cocci have a regular spherical shape. Some cocci, after dividing in the same plane, remain associated in pairs. These are diplococci. Less commonly, they are somewhat pointed, like pneumococci - the causative agents of bacterial pneumonia (Fig. 2.1), or have the appearance of coffee beans or beans, like menigococci - the causative agents of meningitis. Gonococci, the causative agents of the venereal disease gonorrhea, look exactly the same (Fig. 2.2).

Based on the location of the cells after division, cocci can be divided into several groups; in some of them, after division, the cells diverge and are located singly. Such forms are called micrococci. Sometimes cocci, when dividing, form clusters resembling bunches of grapes. Such forms are called staphylococci (Fig. 2.3).

Rice. 2.1.

In streptococci, division also occurs in the same plane, but the cells are not separated from each other, and therefore chains of different lengths are formed (Fig. 2.4).

Rice. 2.4.

Some cocci divide in three mutually perpendicular planes, which leads to the formation of peculiar cubic-shaped clusters. Such clusters of cocci are called sardines (Fig. 2.5). If, after division in two mutually perpendicular planes, the cells are arranged in the form of combinations of four cocci, then such clusters are called tetracocci (Fig. 2.6).

Rice. 2.5.

Rice. 2.6.

Rod-shaped bacteria have rounded or pointed ends. The arrangement of cells after division is also varied - single rods, two at a time, in chains, etc. (Fig. 2.7).

Rice. 2.7.

Convoluted, or spiral, bacteria are often found. There are two groups of convoluted forms of bacteria. The first group includes spirilla, which have the shape of long curved (one or several curls) rods, and vibrios, which represent only part of a spiral turn and look like a comma. The second group of convoluted bacteria - spirochetes - are long and thin cells with a large number of small curls (Fig. 2.8).

Bacterial cells are very small, measuring in micrometers (μm). Cocci have a diameter of about 0.5-1.0 microns. The width of rod-shaped bacteria ranges from 0.5 to 1.0 microns, and the length can reach several tens of microns. The size of bacteria can vary significantly depending on temperature, medium composition, etc.

The bacterial cell is surrounded by a membrane. The cytoplasm contains the nuclear apparatus, vacuoles, analogs of mitochondria - mesosomes, ribosomes, as well as various types of inclusions usually formed during the metabolic process (Fig. 2.9).

The cell membrane has a certain rigidity (rigidity), at the same time elasticity and the ability to bend. The cell membrane can be destroyed by ultrasound, the enzyme lysozyme, a thin needle, etc. In this case, the contents of the cell - the cytoplasm - with its inclusions flow out and acquire a spherical shape. It follows that the membrane gives the bacterial cell a certain shape.

Cell membranes exhibit a certain organization. The mass of the cell membrane makes up about 20% of the total mass of the cell. The cell membrane is often surrounded by a mucous layer, which varies among individual bacteria in both thickness and consistency. This layer is called a capsule (Fig. 2.10).

Rice. 2.10.

Based on the chemical composition, bacterial capsules can be divided into 2 types. One type of capsule consists of polysaccharides - dextrans, the other of polypeptides. Many bacteria contain peptides in their capsule, consisting mainly of chains of glutamic acid molecules.

The capsule protects the cell from the adverse effects of the surrounding environment. Capsulated bacteria can live in environments in which the growth of non-capsulated bacteria is limited. In some cases, the capsule substance can be used by bacteria as a food reserve when other food is not available.

The outer layer of cytoplasm, the cytoplasmic membrane, is closely adjacent to the cell wall of the bacterial cell. This non-rigid structure, sometimes called the cell's osmotic barrier, acts as a semi-permeable membrane and controls the transport of ions and molecules into and out of the cell. The cytoplasmic membrane makes up about 10% of the cell's dry weight, consists of polyproteins and contains up to 75% of the cell's lipids. Often the membrane gives rise to intracytoplasmic branches (invaginations), leading to the formation of special bodies - mesosomes.

The membrane and mesosomes perform functions characteristic of mitochondria of higher organisms, in which various enzyme systems are localized.

Beneath the cytoplasmic membrane is the cytoplasm. It is usually considered as a colloidal system consisting of water, proteins, fats, carbohydrates, mineral compounds and other substances, the ratio of which depends on the type of bacteria and their age.

Detailed studies of the micromolecular organization and submicroscopic structure of the cytoplasm revealed its fine-granular nature. Many of these granules are ribosomes, particles rich in protein and ribonucleic acid. A bacterial cell contains approximately 10,000 ribosomes, which carry out protein synthesis in the bacterial cell.

The cytoplasm of bacteria contains granules of reserve nutrients. As reserve nutrients, substances consisting of carbohydrates - glycogen (animal starch) or granulosa (close to starch) - can accumulate in bacterial cells. If there is insufficient supply of carbon-containing substances to the environment, glycogen or granulosa gradually disappear from the bacterial cells.

Some types of bacteria accumulate fat and volutin in their cells. The latter consists of inorganic polyphosphates and polymetaphosphates, as well as substances close to nucleic acids. Volutin is found in the form of large, clearly visible granules, formed in large quantities on media rich in glycerol or carbohydrates.

The nuclear apparatus (sometimes called the nucleoid) is located in the cytoplasm of bacterial cells. In bacteria, discrete (discontinuous) shaped structures are constantly found that contain deoxyribonucleic acid (DNA) as well as protein and have the function of the nucleus or, more precisely, the chromosomes of higher forms of organisms. Typically, a nuclear formation (one per cell) is located in the central part of the internal contents of the bacterial cell. Unlike the cells of highly organized organisms, the nucleoid of bacteria is not separated from the cytoplasm by a membrane.

Many bacteria move with the help of special thread-like appendages - flagella, which determine the mobility of bacteria due to their spiral wave-like movements due to rhythmic contractions (Fig. 2.11).

Rice. 2.11.

Cocci, with the exception of certain species, do not have flagella. Among the cylindrical forms of bacteria, approximately half have flagella. Of the spiral-shaped bacteria, most are motile.

Bacteria with one flagellum are called monotrichous; bacteria with a bundle of flagella at one or both ends of the body are called lophotrichous. Peritrichous are bacteria that have flagella over the entire surface of their body. The number of flagella in different species of bacteria can vary significantly. For example, vibrios have 1-3 flagella, while rod-shaped bacteria have 50 to 100 flagella.

The thickness of the flagella is about 0.01 microns, and their length is many times greater than the length of the bacteria’s body. Chemically, flagella are protein and are denatured when heated.

Flagella are not a vital structure for a bacterial cell. Thus, bacteria with flagella can be grown under conditions in which they do not develop flagella. In motile bacteria, “phase variations” are observed, i.e. flagella are present during one phase of development and absent during another. Bacterial flagella can be destroyed, but the cell will remain viable.

Flagella originate from a dense body in the cytoplasm, but at the same time they are attached not only to the cytoplasmic membrane, but also to the cellular membrane. Protoplasts freed from the cell membrane retain flagella.

Bacterial cells - monotrichs, moving with the help of a flagellum along their axis, make a wave-like movement. Peritrichous animals exhibit vigorous tumbling.

The speed of movement of bacterial cells depends on the characteristics of their movement apparatus and the properties of the medium - its viscosity, temperature, pH, osmotic pressure, etc. Some bacteria can move, under favorable conditions, a distance exceeding the size of the cell by 10-15 times. Most bacteria travel a distance in a second equal to the size of their cell.

In addition to flagella, bacterial cells can have straight processes - fimbriae. Fimbriae are much shorter and thinner than flagella, but are more numerous and are found in both motile and immobile organisms.

Some bacteria are capable of forming spores (endospores), spherical or elliptical bodies that are very resistant to adverse conditions. The spores refract light and are clearly visible under a light microscope. Typically, one spore is formed in a cell - an endospore. Disputes can be considered as an adaptation of the body to endure unfavorable external conditions. They are not reproductive organs (Fig. 2.12).

Spore formation depends on growth conditions. Spores can remain alive under conditions where vegetative cells, i.e. those that do not form a spore die. Most spores tolerate drying well; many spores cannot be killed even by boiling for several hours. In a dry state, spores die only with strong heating (15-160 ° C) for several hours. Spores of certain types of bacteria are distinguished by their heat resistance.

Rice. 2.12. Bacterial spores

The spores contain little water (due to dehydration), which protects the proteins from denaturation at high temperatures. The resistance of spores to unfavorable factors is also determined by the special structural form that the spore protein takes during the process of sporulation.

The diameter of the spore is approximately equal to the diameter of the cell in which it was formed, or slightly exceeds it. In some bacteria, a spore forms at the end of the cell, which expands somewhat. In this case, the cell takes on the appearance of a drumstick. In other bacteria, spores are formed in the center of the cell, which either does not change shape (genus Bacillus), or in the middle it expands and takes the form of a spindle (genus Clostridium). The vegetative part of the cell collapses and disappears, leaving only the light-refracting spore. The spore is difficult to stain with dyes.

Finding itself in favorable conditions, the spore begins to “germinate.” At the same time, it swells not only as a result of water absorption, but also due to cell growth due to reserve material. Then the shells, under the influence of pressure caused by growth, rupture and crack. A new vegetative cell appears. The manner in which the cell emerges from the spore varies among species and can be used as a species characteristic.

There are microorganisms that form cells that are relatively resistant to unfavorable conditions - cysts. Cysts are characterized by a thickened membrane.

Due to the rigidity of its wall, the cell maintains its shape: spherical, rod-shaped or convoluted. The membrane protects the cell, maintaining its structural integrity when external conditions change, in particular during osmotic influences. Along with the membrane, it acts as a semi-permeable barrier, allowing selective penetration of nutrients from the environment and the release of high-molecular compounds - toxins or enzymes involved in the extracellular digestion of substrates. The cell wall determines the antigen specificity of species, is the site of adsorption of phages on the cell, and is involved in the processes of movement and division.

When studying the chemical composition of the cell walls of gram-positive and gram-negative bacteria, significant differences in their qualitative and quantitative composition were revealed (Fig. 2.13).

The same heteropolymer, peptidoglycan, is responsible for the mechanical strength of the wall in these groups of microorganisms, although its quantitative content and localization are different. Attack cell wall components such as teichoic acids are found in the walls of only gram-positive bacteria. Electron microscopic examination of sections of the surface layers of gram-positive and gram-negative bacteria also confirmed the heterogeneity of the structure of their cell walls.

Morphology of bacteria (prokaryotes)

Bacteria (Greek bakterion - stick) are microorganisms with a prokaryotic type of structure. Mostly these are single-celled organisms, but there are many forms consisting of many cells. The term "prokaryotes" is equivalent to the term "bacteria".

Shape and size of bacteria

Based on the shape of the cells, bacteria are divided into three main groups: spherical, or cocci, rod-shaped and convoluted (Fig. 1).

Cocci (Greek kokkos - grain, Lat coccus - berry). They have a spherical shape in the form of a regular ball, ellipse, bean, lancet. Depending on the relative position of the cells after division, they are distinguished: micrococci, or monococci, staphylococci, diplococci, streptococci, tetracocci and sarcina.

Rice. 1. Basic forms of bacteria

a - micrococci; b - diplococci and tetracocci; c - sarcins; d - streptococci; d - staphylococci; f. g - rod-shaped bacteria; h - vibrios; and - spirilla; k - spirochetes

Micrococci (lat. micrococcus - small) are divided in equal planes and are located singly, in pairs or randomly. Saprophytes live in soil, water, and air. For example, Micrococcus luteus.

Staphylococci (Greek staphyle - bunch of grapes) are cocci that divide in different planes and are located in asymmetrical clusters, sometimes singly, in pairs, or in tetrads. Saprophytes and pathogens. For example, Staphylococcus aureus.

Diplococci (Greek diploos - double) are divided in one plane, forming cocci connected in pairs. For example, Azotobacter chroococcum.

Streptococci (Greek streptos - chain) - cocci arranged in the form of a chain, there are single and paired cells, sometimes tetrads. Formed by division in one plane. Saprophytes and pathogens. For example, Streptococcus pyogenes.

Tetracocci (Greek tetra - four) are cocci that are divided in two mutually perpendicular planes and are arranged in groups of four.

Sarcines (lat. sarcio - I bind) are cocci that divide in three mutually perpendicular planes and form regular packets of 8-16 cells or more. Saprophytes are found in the air, soil, and intestines of animals and humans. For example, Sarcina ureae.

Rod-shaped bacteria. This is the largest group of prokaryotes. They have axial symmetry and a cylindrical body shape with rounded or pointed ends. Rod-shaped forms are divided into two groups: non-spore-forming rods - bacteria (Bacterium) and rods that form spores - bacilli (Bacillus). Rods in which the diameter of the spore exceeds the width of the vegetative cell are usually called clostridia.

Depending on the relative arrangement of cells, rod-shaped bacteria are divided into single and unsystematic clusters, diplobacteria and diplobacillus (located in pairs), as well as streptobacteria and streptobacilli (forms forming long or short chains). Saprophytes and pathogenic species. For example, Bacillus anthracis, Clostridium tetani.

Rod-shaped forms also include corynebacteria and fusobacteria.

Corynebacteria….Greek. korync - mace) - straight or curved sticks with club-shaped thickenings at the ends. Saprophytes, pathogenic for animals and humans. For example, Corynebacterium pseudotuberculosis and others.

Fusobacteria are long, thick rods with pointed ends. There are pathogenic species - the causative agent of necrobacterium necrophorum (Fusobacterium necrophorum).

Twisted bacteria. They have spiral symmetry. These include vibrios, spirilla and spirochetes.

Vibrios (lat. vibrio - wriggle). Vibrio cells have a cylindrical curved shape, forming 1/4-1/2 of a spiral curl, and resemble a comma. Saprophytes and pathogens. For example, Vibrio cholerae.

Spirilla (Latin, spira - bend) are bacteria that have the shape of spirally twisted rods with 4-6 turns. They live in fresh and sea water. Mainly saprophytes (Spirillum volutans); Pathogenic species include S. minus and Campylobacter fetus.

Spirochetes (spirochaeta; Greek speira - bend and chaite - long hair) are prokaryotes with a spirally convoluted shape. In spirochetes, two types of coils are detected: primary - formed by the bends of the protoplasmic cylinder, and secondary - representing the bends of the entire body. Spirochetes are elastic, spiral-shaped long cells consisting of an axial filament (axistyl), cytoplasm with ribosomes and inclusions, nucleoid, mesosomes, cytoplasmic membrane and cell wall. The thin elastic cell wall consists of an outer lipoprotein membrane and a discontinuous layer of paptidoglycan. The axial filament is stretched over the entire length of the cell, performs locomotor and supporting functions, and contains a bundle of 2-150 axial (supporting) fibrils, consisting of the amino sugar cutin. The number and size of fibrils varies among different species. The protoplasmic cylinder is packed in a spiral shape and is surrounded by axial fibrils attached to disks at its ends. The fibrils are contained in the periplast (between the cytoplasmic membrane and the cell wall). The movement of spirochetes is carried out due to the active contraction of the axial filament and protoplasmic cylinder; forms of movement are varied: rotational, translational, flexion.

They reproduce by transverse division. Under unfavorable conditions, spirochetes can transform into a cyst - a shortened and coiled cell surrounded by a durable membrane.

According to morphology (size, number and shape of whorls), the number of axial fibrils, the nature of movement, the type of biological oxidation, ecology, pathogenicity within the group of spirochetes, they differentiate: spirochetes, cristispires, treponemas, borrelia and leptospira.

Spirochetes and Christispira live in open bodies of water, silt, and sewage; non-pathogenic for vertebrates. Christyspires are giant prokaryotes (28-150 µm) of a spirally curved shape with a flat granular keel-shaped membrane (crista) running along the cell body. The number of fibrils is more than 100.

Treponomas are spirally twisted elastic bacteria, size 0.1-0.5, 5-20 microns; the axial filament consists of 1 or 4 fibrils; uniform or uneven curls are well defined; mobile. The type species is Treponema pallidum.

Borrelia are convoluted filamentous bacteria, size 0.2-0.5 X 5-30 microns; the axial filament consists of 15-20 parallel fibrils.

Leptospires are spiral-shaped bacteria with a diameter of 0.1-0.25 microns and a length of 6-30 microns, forming about 20 small, closely spaced primary curls and 1-2 secondary ones, giving the cell the shape of the letters G, S, C. The axial thread consists of 2 fibrils. The main type of movement is rotational-translational. For example, Leptospira interrogans.

Bacteria are not visible to the naked eye. Therefore, light and electron microscopes are used to study them. Bacterial cells are measured in micrometers (1 µm = 10" m), elements of a fine structure - in nanometers (1 nm = 10 m). The resolution limit of a light microscope is 0.2 µm, modern models of electron microscopes are 0.15-0.3 nm . The average sizes of prokaryotes are in the range of 0.5-3 microns. The most stable are cocci - their size is 0.5-2 microns. Rod-shaped forms are usually 2-10 long and 0.5-1 microns wide, small rods are 0.7-1 microns, respectively. 1.5 and 0.2-0.4 microns.

In 1967, Adler described mini-cells. They are approximately 10 times smaller than the original bacteria, do not contain chromosomal DNA and have only plasmid DNA. Among the bacteria there may be giants reaching a length of 125 microns or more. The dimensions of the spirochetes are 0.2-0.75 x 5-500 microns.