Microorganisms are a large collective group, within which representatives may differ in cellular organization, morphology and metabolic capabilities, but are united by microscopic sizes. Therefore, the term "microorganism" has no taxonomic meaning. Representatives of the world of microbes belong to a variety of taxonomic groups, the other members of which can be multicellular organisms, sometimes gigantic. For example, lower mold fungi are related to cap mushrooms, and microalgae are combined with such large specimens as kelp. Microorganisms are the largest group in terms of the number of representatives and its members are ubiquitous. Microorganisms have all known types of metabolism.

Ways to classify microorganisms

The accumulation of vast factual material required the introduction of rules for describing objects and distributing them into groups. For the possibility of comparing the results obtained by different researchers, and the convenience of work, it became necessary to classify microorganisms. Classification is understood as the assignment of a particular biological object to a certain group of homogeneity (taxon) according to the totality of its inherent features.

The relationship of subordination and the relationship of taxa of different levels is studied by systematics . In the modern classification of microorganisms, the following hierarchy of taxa is adopted: domain, phylum, class, order, family, genus, species. The species is the basic taxonomic unit. Microbiologists use a binomial system for designating an object (nomenclature), including generic and specific names, for example, Escherichia coli, Saccharomyces cerevisiae, Pseudomonas aeruginosa etc. In some cases, the use of historically established Russian-language names (E. coli, baker's yeast, Pseudomonas aeruginosa) is allowed.

For classification, it is important to agree on a set of criteria that will be decisive when combining objects into a group. Most microorganisms have an extremely simple and universal structure; therefore, morphological descriptions are not enough to divide them into taxa. Researchers were forced to use the functional characteristics of microorganisms, i.e. note the peculiarities of their metabolism. At the same time, depending on the approach, the signs could have unequal significance (some were mandatory for placement in this group, while others could vary).

At present, it is impossible to classify a microbiological object without examining the totality of morphophysiological, biochemical, and molecular biological data. When determining an unknown microorganism (identification), the following properties are examined:

Cell cytology (first of all, assignment to pro- or eukaryotes);
Morphology of cells and colonies (on certain media and under certain conditions);
Cultural characteristics (character of growth on solid and liquid media);
Physiological properties (ability to use various substrates, relation to temperature, aeration, pH, etc.);
Biochemical properties (presence of certain metabolic pathways);
Molecular biological properties (nucleotide sequence of 16S rRNA, content of GC-AT pairs in mol.%, the possibility of hybridization of nucleic acids with the material of typical strains);
Chemotaxonomic properties (chemical composition of various compounds and structures, for example, the spectrum of fatty and teichoic acids in actinobacteria, mycolic acids in nocardia, mycobacteria, corynebacteria);
Serological properties based on antigen-antibody reactions (especially for pathogens);
Sensitivity to specific phages (phage typing).

Sometimes the presence of extrachromosomal elements in a microorganism, including silent (cryptic) plasmids, is noted. It should be remembered that plasmids can be easily lost.

When identifying prokaryotic microorganisms, modern researchers rely on the instructions of the Bergey's Manual of Systematic Bacteriology and use the Bergey key.

Currently, there are several main ways to classify living objects, including microorganisms.

Formal numerical classification considers all signs of an organism to be of equal importance. The criteria to be taken into account must be alternative, i.e. present (+) or (-) absent from a particular object. The accuracy of placing it in this group will depend on the completeness of the study of the organism. To quantify the degree of similarity and difference between objects, special computer programs have been developed that compare organisms according to a set of studied traits. Similar organisms are combined into clusters.

For morphophysiological classification, it is necessary to study the totality of morphological features and characteristics of the metabolism of organisms. At the same time, the different significance of the applied criteria is taken into account: some properties are considered mandatory, significant for the object, while others may be present to varying degrees or completely absent. To place microorganisms in a group and give them a name, first determine the type of cellular organization, describe the morphology of cells and colonies, as well as the nature of growth on certain media and under certain conditions. The functional characteristics of the object include the possibility of using various nutrients, attitude to the physical and chemical factors of the environment, as well as the identification of ways to obtain energy and reactions of constructive exchange. Some microorganisms require chemotaxonomic studies. Pathogenic microorganisms are usually subjected to serodiagnosis. The results of all these tests are used when working with the determinant. At present, to identify prokaryotic microorganisms, researchers use a determinant named after the American bacteriologist Burgee, who in 1923 proposed the basis for such a classification.

Molecular genetic classification involves the analysis of the molecular structure of important biopolymers. Such a molecule must be conserved and meaningful to the underlying life process. University of Illinois professor Carl Vöz suggested taking prokaryotic 16S ribosomal RNA (18S rRNA for eukaryotic organisms) as a basis. This molecule is part of the ribosomes, which in all living beings are responsible for the most important life process - protein synthesis. The apparatus of protein synthesis changes slightly over time, since any significant disturbance can lead to cell death. Therefore, in rRNA molecules different organisms most nucleotides are unchanged, and the part that changes in the course of evolution is unique to a particular organism. 16S rRNA consists of 1500 nucleotides, of which 900 are conserved; it possesses sufficiently large, but not excessive information and can be considered a kind of biological genetic "chronometer". Comparing with special computer programs nucleotide sequences of this molecule in different organisms, it is possible to obtain similarity groups of biological objects, reflecting their family ties and evolutionary development. Based on many comparisons, a phylogenetic tree was built, where all representatives of the living world are divided into three large domains (empires, superkingdoms): Bacteria, Archaea and Eukarya. The Bacteria and Archaea domains contain only prokaryotic organisms, while the Eukarya domain includes all eukaryotes, both unicellular and multicellular, including humans. At the same time, it was proved that mitochondria and chloroplasts have a prokaryotic symbiotic origin. Researchers send the nucleotide sequences of the studied organisms to the worldwide computer genebank, the data of which are intended for comparison with the sequences of each newly isolated organism.

Currently, to identify a specific microorganism, its pure culture is first isolated and the 16S rRNA nucleotide sequence is analyzed. It allows you to determine the place of the microorganism on the phylogenetic tree, and then the determination of the species name is carried out by traditional microbiological methods. At the same time, 90% of matches indicate belonging to a certain genus, 97% - to a certain species. To clarify the taxonomic affiliation, DNA-DNA hybridization is carried out, which gives > 30% coincidence within the genus and > 70% within the species.

For a clearer differentiation of microorganisms at the level of genus and species, it is proposed to use polyphyletic (polyphase) taxonomy, when, along with the determination of nucleotide sequences, information of different levels, up to ecological, is used. At the same time, a preliminary search for groups of similar strains and the determination of the phylogenetic positions of these groups are carried out, differences between the groups and their nearest neighbors are recorded, and data are collected to differentiate the groups.

Main groups of eukaryotic microorganisms

IN Eukarya domain there are three groups containing microscopic objects. These are algae, protozoa and fungi.

Seaweed("growing in water") are unicellular, colonial or multicellular phototrophs that carry out oxygenic photosynthesis. The molecular genetic classification of algae is under development, therefore, for practical purposes, algae are classified according to the composition of pigments, reserve substances, the structure of the cell wall, the presence of mobility and the method of reproduction. Microbiological objects are traditionally considered unicellular representatives of dinoflagellates, diatoms, euglenoids and green algae, as well as their colorless forms that grow in the dark and have lost pigments. All algae form chlorophyll A and various forms of carotenoids, and representatives of the groups differ in their ability to synthesize other forms of chlorophylls and phycobilins. Cell staining in different colors: green, brown, red, golden, - depends on the combination of pigments in a particular species. Diatoms are unicellular planktonic forms that have a characteristic cell wall in the form of a silicon bivalve shell. Some representatives can move by sliding. They reproduce both asexually and sexually. Unicellular euglenoid algae live in freshwater bodies and move with the help of flagella. They lack cell wall. Can grow in the dark due to oxidation organic matter. The cell wall of dinoflagellates is made up of cellulose. These planktonic unicellular algae have two lateral flagella. Microscopic representatives of green algae live in fresh and marine water bodies, in the soil and on the surface of various terrestrial objects. They can be motionless or move with the help of flagella. Green microalgae have a cellulose cell wall and store starch in their cells. They are able to reproduce both asexually and sexually.

Mushrooms are divided into groups according to the characteristics of their reproduction. Imperfect fungi include representatives in which no sexual reproduction. Traditional microbiological objects - types of genera Penicillium, Aspergillus, Candida, Rhodotorula and others are included in this group. The group of zygomycetes is made up of fungi that have coenocytic mycelium and form a zygospore by the fusion of two parental hyphae during the sexual process. Known genera of Zygomycetes are Mucor and Rhizopus. Mushrooms that form a special bag (ask) for sporulation are called ascomycetes. They have a septate mycelium, and during asexual reproduction they form conidia (chains of spores collected in brushes or heads). This group includes genera Neurospora, Saccharomyces, Lipomyces, Cryptococcus. Some yeasts and most higher cap mushrooms belong to the basidiomycetes. During sexual reproduction, they form a special swollen hypha (basidia), which forms outgrowths with spores. The mycelium of basidiomycetes is divided by partitions.

An important place in human economic activity is occupied by representatives of the combined non-taxonomic group of yeasts. It includes mushrooms, which are characterized by the absence or a significant reduction in the mycelial stage of growth. Best known as yeast representatives of the genera Saccharomyces, Lipomyces, Candida, Rhodotorula, Pichia. The morphology and metabolism of yeasts largely depends on the growing conditions. Many yeasts exist for a long time as separate immobile cells and reproduce by budding. Most yeasts are facultative anaerobes. There are also pathogenic species among yeasts (for example, candida albicans is the causative agent of "thrush").

Main groups of prokaryotic microorganisms

Prokaryotic microorganisms are grouped into two separate domains: Bacteria and Archaea. The division of these groups occurred based on the results of comparison of 16S rRNA nucleotide sequences, as well as due to significant differences in the composition of cell walls, lipids, and due to metabolic features. Archaea differ from bacteria and eukaria in a number of essential ways. In ordinary lipids, glycerol is linked by an ester bond to fatty acids, and in archaea, by an ether bond to the isoprenoid C 20 alcohol, phytanol. . Phytanol chains may contain five-membered rings. Archaeal lipids are able to form tetramers (C40), so the membrane composed of tetramers is more rigid than a traditional bilayer due to the lack of internal space. Archaea can have both conventional bilayer and rigid monolayer membranes. The more extreme the conditions of their habitat, the more monolayer regions are contained in their CPM.

In archaea, peptidoglycan (murein) cell walls typical of bacteria have not been found. The composition of the cell walls of archaea may include another heteropolysaccharide - pseudomurein, which lacks N-acetylmuramic acid. Some archaea may have a protein S-layer on top of the CPM as a cell wall. Another variant of archaeal organization is the complete absence of a cell wall, when the membrane is almost entirely represented by a rigid monolayer of tetramers, reinforced by a large number of five-membered rings, for example, as in Thermoplasma.

In a number of ways, archaea are closer to eukaria than to bacteria. So, like eukaryotes, archaea have intron regions in DNA, as well as histone-like proteins associated with nucleic acids. Halophilic archaea are able to carry out chlorophyll-free photosynthesis associated with the functioning of a special protein, bacteriorhodopsin, which is similar in many properties to rhodopsin in the retina of animals. Many archaea live in extreme environments and grow sparsely. However, in such habitats they have few competitors, which has allowed them to survive to the present day.

Archaea domain divided into three phyla: Euryarchaeota, Crenarchaeota and Korarchaeota. The first includes ubiquitous microorganisms of several physiological and systematic groups. These are methanogens - strict anaerobes that live in the bottom sediments of freshwater zones rich in organic matter, or in the rumen of ruminants. Extreme halophiles (haloarchaea) are also widespread, growing at high salt concentrations and capable of performing a special type of photosynthesis with the help of bacteriorhodopsin, which works like a proton pump in the light. Thermoplasmas living in hot acidic springs and obligately anaerobic thermococci develop at high temperatures, and thermoplasmas are devoid of cell walls. This phylum also includes extremely thermophilic sulfate reducers.

The second phylum includes microorganisms that live in very specific places with narrow boundaries for the values of physicochemical factors. These are extremophiles dependent on sulfur compounds, whose optimum pH and growth temperatures are characterized by extreme values.

The third phylum is reserved for groups whose representatives are not amenable, but for which the sequences of genes encoding the 16S rRNA molecule are known.

Domain Bacteria combines prokaryotic microorganisms that have typical features of bacteria, in particular, cell membranes containing peptidoglycan. Currently, the domain is divided into 23 phyla, which contain cultivated representatives, all or part of which are obtained as pure cultures.

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1. Fundamentals of microbiology

Microbiology as an independent science , which has its own objects and methods of research, was formed in the second half of the 19th century thanks to the works PasteurKoch, Erlich, Mechnikov, Ru and others, but also at the present time, as well as those closely related to it, biotechnology And Genetic Engineering is constantly and intensively developing.

Born as the science ofpathogens , i.e. as a branch of medicine, to date depending on the tasks to be solveddivided by :

industrial;

agricultural;

veterinary;

· sanitary;

medical microbiology.

Subject study medical microbiology are microorganisms — representatives of the normal microflora of the human body and pathogens of various human diseases, and methods laboratory diagnostics , specific prevention And etiotropic therapy the diseases they cause.

2. Classification (systematics) of microorganisms

Microorganisms — This organisms, invisible to the naked eye due to their small size. This 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 belong tothree kingdoms:

· Vira- they include viruses;

· Eucariotae- these include protozoa and fungi;

· Procariotae- these include true bacteria, rickettsia, chlamydia,

mycoplasmas, spirochetes, actinomycetes.

Main differences prokaryotes from eukaryote are that prokaryotes do not have :

morphologically arranged nuclei(No nuclear membrane and missing nucleolus), its equivalent is nucleoid, or genefor representing 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 features or organelle, characteristic of many, but not all prokaryotes, which allow distinguish them from eukaryotes :

numerous invagination of the cytoplasmic membrane, which are called mesosomes , they are bound to the nucleoid and involved in cell division, spore formation, And breathing bacterial cell ;

specific cell wall component— murein , according to the chemical structure is peptidoglycan(diaminopiemic acid);

· plasmids — autonomously replicating circular double-stranded DNA molecules with a smaller molecular weight than the bacterial chromosome. They are located along with the nucleoid in the cytoplasm, although they can be integrated into it, and carry hereditary information, which is not vital for a microbial cell, but providing her one or the other selective advantages in the environment. Most famous plasmids :

- (F-plasmids), providing conjugation transfer between bacteria;

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

As well as for plants and animals, the name of microorganisms is used binary nomenclature , - that is generic and specific name, but if the researchers cannot determine the species affiliation and only the belonging to the genus is determined, then the term "species" is used. Most often this takes place when identifying microorganisms with non-traditional nutritional needs or living conditions.

Name kind usually either based on the morphological trait of the corresponding microorganism (eg, Staphylococcus, Vibrio, Mycobacterium) or are derived from the name of the author who discovered or studied this pathogen (eg, Neisseria, Shigella, Escherichia, Rickettsia, Gardnerella).

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

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

Kingdom of prokaryotes includes department of cyanobacteria And department of eubacteria, which, in turn, subdivided into orders :

Bacteria proper (Departments Gracilicutes, Firmicutes, Tenericutes, Mendosicutes);

actinomycetes;

· spirochetes;

rickettsia;

chlamydia.

bacteria - This prokaryotic, mainly unicellular microorganisms, which may Also form associations(groups) similar cells, characterized cellular but not organismic similarities.

Orders subdivided into groups. The main taxonomic criteria , which make it possible to classify bacterial strains as one or another group, are :

morphology of microbial cells (cocci, rods, convoluted);

relation to Gram stain - tinctorial properties (gram-positive and gram-negative);

type of biological oxidation - aerobes, facultative anaerobes, obligate anaerobes;

ability to spore formation.

Further group differentiation on families, genera and species, that are main taxonomic category, is carried out on the basis of study of biochemical properties V. This principle is the basis classification of bacteria given in special guidelines — determinants of bacteria .

View is an evolutionarily established set of individuals with a single genotype, which under standard conditions manifested by similar morphological, physiological, biochemical features. For pathogenic bacteria the definition of "type" is supplemented by the ability to cause certain nosological forms of diseases. There is an intraspecific differentiation of bacteria into variants:

· By biological properties(biovars or biotypes);

By biochemical activity (enzyme products);

By antigenic structure (serovars or serotypes);

By sensitivity to bacteriophages (fagovars or phage types);

resistance to antibiotics (resistance products).

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

culture - This visible to the eye collection of bacteria on nutrient media. cultures can be clean () And mixed (collection of two or more species of bacteria).

Strain - This a group of bacteria of the same species allocated from different sources or from one source to different time . Strains may differ in some characteristics that do not go beyond the characteristics of the species.

Clone - This a group of bacteria that are the offspring of a single cell.

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Systematics of microorganisms.

Page 1 of 26Next ⇒

Systematics- distribution of microorganisms according to their origin and biological similarity.

Systematics deals with a comprehensive description species organisms, elucidating the degree of kinship between them and combining them into classification units of different levels of kinship - taxa. The main issues addressed in systematics (three aspects, three whales of systematics) - classification, identification and nomenclature.

Classification- distribution (unification) of organisms in accordance with their common properties(similar genotypic and phentypic characters) for different taxa.

Taxonomy- 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 the modern view species in microbiology

It is based on the use of the maximum number of compared features and mathematical accounting for the degree of correspondence.

Gram stain.

substrates

autotrophs, heterotrophs), nitrogen ( .

8.Ability to sporulation, the nature of the dispute.

In recent decades, for the classification of microorganisms, in addition to their phenotypic characteristics (see.

pp.1-12), various genetic methods are used more and more widely and effectively (study of the genotype - genotypic properties).

Medical microbiology. Medical microbiology

Identification.

Nomenclature-

Strain serotypes (serovariants) abbreviated serovars) fagotypes, biochemical properties - chemovars biovars etc.

The colony- a visible isolated structure during the reproduction of bacteria on dense nutrient media, it can develop from one or more parental cells.

If the colony developed from one parent cell, then the offspring is called clone.

culture

cultures.

Morphology of bacteria.

micron) x 2-3 µm.

2. Rod-shaped.

3.Corrected.

4. Filiform.

coccoid bacteria (cocci)

1.micrococci.

2.Diplococci.

3.Streptococci.

4.Tetracocci. Division in two mutually perpendicular planes with the formation of tetrads (i.e., four cells each).

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 lat. - a bunch of grapes).

They divide randomly in different planes, forming clusters resembling bunches of grapes. They cause numerous diseases, primarily purulent-inflammatory.

2.Bacilli - aerobic spore-forming microbes.

The spore diameter usually does not exceed the size (“width”) of the cell (endospore).

It must be borne 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.

Main groups of bacteria Genera of bacteria

gliding-

Shie bacteria

spirochetes Borrelia, Leptospira

eubacteria

myces, Nocardia, Strep-

B. Simple unicellular

2/ free-living

gram positive:

cocci Streptococcus, Staphy-

teria, Erysipelothrix

spore-forming rods

b. gram negative:

cocci Neisseria

non-intestinal coli

including spiral shape Spirillum

Yersinia Francisella,

Haemophilus, Borde-

coli

facultative anaerobes Escherichia, Salmone-

lla, Shigella, Klebsiel-

la, Proteus, Vibrio

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2. Systematics and nomenclature of microorganisms

The term "taxonomy" is sometimes used as a synonym for the concept of "taxonomy of microorganisms".

At present, there is no universal, only correct classification.

Depending on the task, micro-organisms can be classified by morphological features (rods, cocci, convoluted, etc.), by tinctorial features (gram-positive, gram-negative, etc.), by physiological features (thermophilic , psychrophilic, acidophilic, aerobic, etc.), according to ecological characteristics (nitrogen-fixing, nitrifying, sulfate-reducing, cellulose-destroying, etc.), according to interspecific relationships (antagonists, synergists, commensals, etc.), according to taxis species, genotypic and phylogenetic characters.

Microorganisms are also classified according to the degree of danger to humans, animals and the environment. Thus, the classification of microorganisms is a subjective processing of objective characteristics.

Modern taxonomy of microorganisms includes three main areas:

Characterization of microorganisms- Obtaining all kinds of information about the properties and parameters necessary to assign the determined microorganisms to a particular taxon.

Classification or taxonomy, i.e. the process of ordered arrangement of microorganisms into taxonomic groups based on similarity.

3. Nomenclature— assignment of scientific names to taxonomic groups (taxons).

The basic taxonomic unit in the taxonomy of micro-organisms is view.

According to general biological concepts, a species is a group of organisms close to each other, having a common root of origin and at this stage of evolution characterized by certain morphological, biochemical and physiological features, isolated by selection from other species and adapted to a specific habitat. Important specific feature is the ability of organisms to interbreed and produce offspring.

The definition of a species in bacteria is fundamentally different from the classical definition of a biological species, since they do not have a sexual mode of reproduction.

According to modern concepts, closely related organisms, with a 70% level of DNA homology and similar in terms of morphological, biochemical and physiological characteristics, are classified as one type of bacteria.

In the hierarchical classification of microorganisms, the following taxonomic categories are also used: subspecies- a group of closely related similar organisms inside kind with a level of DNA homology above 70%; genus- taxonomic group, uniting related species, and further - family, suborder, order, subclass, class, realm And domain(or supra-kingdom).

At present, families and domains are mostly described, while other taxonomic groups are in the process of systematization.

2). Of these, two domains (Bacteria and Archaea) include only representatives of prokaryotes, which are separated into a separate supra-kingdom — Procariolae.

Fig.2. Universal phylogenetic tree of living organisms.

The most accurate, informative, and user-friendly classification system is one in which taxa are defined on the basis of a variety of consistent characteristics obtained using various modern methods.

A similar approach to the selection of taxa is called polyphasic.

The main methods of modern polyphasic taxonomy are: genotypic, phenotypic and phylogenetic.

The genotypic method is dominant in polyphasic taxonomy.

It is based on the study of the C+G composition of DNA, on the study of DNA-rRNA homology, on the establishment of related relationships between microorganisms that are encoded in the nucleotide sequences of the 16S or 23S rRNA genes. For example, when determining the belonging of a microorganism to a certain species, the level of similarity of nucleotide sequences of DNA of about 70% plays a paramount role. Therefore, the genotypic method is often called the method of genomic fingerprinting.

Phenotypic studies are used most often in various schemes for the identification of microorganisms, for the formal description of a taxon, from variety and subspecies to genus and family.

While genotypic data is necessary to place a taxon on a phylogenetic tree and in a classification system, phenotypic characterization provides descriptive information that allows identification of a particular microorganism species. Classical phenotypic characteristics include morphological, physiological, biochemical, chemotaxonomic and serological characteristics of microorganisms.

Morphological features indicate what size and shape the microorganism has (coccus, bacillus, spirilla), whether it has a capsule or spores, whether the cells are combined into chains, tetrads or packages, whether they have flagella and how they are located, whether the cells stain ki according to Gram.

The morphology of bacteria includes the study of cultural properties, i.e. the nature of growth on nutrient media, the shape of colonies on dense nutrient media, pigment formation.

Physiological features characterize the mechanism of metabolism, the method of obtaining energy, the ability of a given microorganism to transform certain substances, its relation to carbon, nitrogen, oxygen, temperature, pH of the environment.

Biochemical signs are determined by the ability of micro-organisms to decompose certain sugars, form hydrogen sulfide, ammonia and other compounds.

Chemotaxonomic features characterize the chemical composition of the cell cytoplasm.

The taxonomic specificity of the composition of fatty acids, lipoproteins, lipopolysaccharides, pigments, polyamines, proteins and other chemical components of the cell is widely used in the classification of microorganisms.

Serological properties, or serotyping, are based on the identification of the variability of the antigenic components of bacterial cells.

Such components can be flagella, fimbriae. capsules, cell wall, enzymes and toxins. To identify the antigenic properties of a bacterial cell, various serological reactions are used: precipitation reaction, complement bonding reaction, precipitation, etc.

Thus, phenotypic characteristics are distinguished by a large volume and variety of information obtained, which is difficult to process manually.

There was a need for a computer, numerical analysis of the data obtained. Numerical (numerical) taxonomy has appeared, which allows using computer programs to analyze the phenotypic and genotypic characteristics of microorganisms. The use of numerical analysis in taxonomic practice is called "computer identification".

Phylogenetic methods (from the Greek phylon - genus, tribe and genesis - origin, occurrence) allow you to trace the process historical development microorganisms both in general and their individual taxonomic groups: species, subspecies, genera, families, suborders, orders, subclasses, classes, kingdoms and domains.

Phylogenetic relationships between microorganisms are studied by the methods of genomic fingerprinting, molecular biology, computer identification.

Based on the obtained data, phylogenetic trees are built, which reflect the evolutionary relationships between microorganisms (Fig. 3). The created phylogenetic trees cannot be used to build a hierarchical classification of microorganisms and do not replace systematics. They are one of its elements.

Nomenclature- deals with issues of precise and uniform names. Ego is a system of names used in a certain field of knowledge.

In accordance with international rules, taxonomic groups of microorganisms are assigned names.

Currently, the name of microorganisms is assigned in accordance with the rules of the International Code of Nomenclature of Bacteria. The competence of the Code extends only to the rules for assigning and using the scientific names of microorganisms. Classification issues are resolved regardless of the Code on the basis of ongoing taxonomic studies.

3. Phylogenetic tree of bacteria.

In microbiology, as in biology, a double (binary) nomenclature, proposed as early as 1760 by Carl Linnaeus, is adopted to designate bacterial species.

The first word is the genus name. Usually this is a Latin word, it is written with capital letter and characterizes any morphological or physiological feature, or the name of the scientist who discovered this microbe. For example, in honor of the French scientist L. Pasteur, the genus "Pasteurella" is named, the American microbiologist Salmon - the genus "Salmonella", the German scientist T.

Escherichia - the genus "Esherichia", the Japanese microbiologist Shiga - the genus "Shigella", the English bacteriologists D. Bruce and S. Erwin - the genera "Brucella" and "Ervinia", the Russian scientists Kuznetsov and Lyambl - the genera "Kuznetsovia" and "Lamblia" and etc. The name of the microorganism genus is usually abbreviated to one or two letters.

The second word denotes a specific epithet in the name of a microorganism and, as a rule, is a derivative of a noun that describes the color of the colony, the source of origin of the microorganism, the process or disease it causes.

The species name is capitalized and never abbreviated. For example, Escherichia coli means that Escherichia live in the intestines, Pasterella pestis means Pasteurella that causes plague, Bordetetia pertussis means Bordetella that causes coughing, Clostridium tetani means Clostridium that causes tetanus, etc.

Vinogradsky and M. Beijerink, taking into account the diversity of bacterial metabolism, suggested that the genus name should reflect the features associated with morphology, ecology, biochemistry and physiology of microorganisms. This is how the names appeared, which are the key to the characterization of the microorganism: Acetobacter (acid-forming bacteria), Nitrosomonas (nitrifying bacteria), Azotobakter (bacteria that fix atmospheric nitrogen), Chromobacterium (pigmented bacteria), B.

stearothermophiliis (wax thermophilic bacteria), etc.

Microorganism identification schemes are a kind of test of the quality of the classification system. For the identification of microorganisms, phenotypic and genotypic methods, methods of computer identification analysis and genomic fingerprinting are widely used.

In 1923 D.

Burgey released the first international bacterial determinant. Subsequent editions have been prepared by the International Committee on the Systematics of Bacteria. The ninth and last US edition of Bergey's Manual of Determinative Bacteriology was published in 1994. The abbreviated name of the Manual is BMDB-9. The Russian translation of BMDB-9 was published in 1997.

It introduces the diversity of prokaryotes and takes a step towards attempts to identify microorganisms isolated from the environment.

According to BMDB-9, bacteria are classified (based on phenotypic traits) into four main categories:

1. Gram-negative eubacteria with cell walls.

2. Gram-positive eubacteria with cell walls.

Eubageria lacking cell walls.

4. Archaebacteria.

The main object in the identification of microorganisms is a pure culture of an isolated bacterium, called a "strain" or "clone".

Strain(from him.

stammen - occur) is a bacterial culture of the same species, isolated from different objects or from the same object at different times, and characterized by minor changes in properties (for example, sensitivity to antibiotics, enzymatic activity, ability to form toxins ). Typically, strains of one species are adapted to a particular habitat.

under the term " bacterial culture» understand the population of microbial cells in a given place and at a given time.

These can be microorganisms grown on a solid or liquid nutrient medium in a laboratory. The culture of microorganisms grown on a dense or liquid nutrient medium from individuals of the same species by successive reseeding of a single colony is called clean.

Pure bacterial cultures obtained from one original cell are called clones(from Greek.

klon - offspring). A clone is a genetically homogeneous population.

A mixed culture is called a culture of heterogeneous microorganisms isolated from the material under study, for example, from water, soil, air.

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Systematics is a science dealing with the classification (distribution) of microorganisms into groups (taxa) in accordance with certain characteristics, their nomenclature and identification. A taxon is a group of organisms that have a given degree of homogeneity.

The basic taxonomic unit in biology is the species. View- this is an evolutionarily established set of individuals of the same genotype with similar morphological, physiological, cultural, biochemical and other features.

Species in microbiology are divided into subspecies or variants, strains and clones. Bacteria options differ in their individual features: morphological (morphovars), biological (biovars), enzymatic (enzyme products), resistance to antibiotics (resistensvars) and bacteriophages (phage vars), antigenic structure (serovars), pathogenicity for certain hosts (pathovars).

Strain- this is a culture of microbes isolated from a specific source (human body, animal, environment) by different authors and at different times.

Taxonomy of bacteria

Clone- a culture of microorganisms obtained from a single individual. Under the term "culture" understand microorganisms grown on a liquid or solid nutrient medium.

There are two principles of taxonomy: phylogenetic, which is based on the establishment of family ties between organisms (taxonomy of higher organisms) and practical(artificial), the purpose of which is to identify the degree of similarity between microorganisms for rapid identification and assignment to certain taxa.

The modern taxonomy of microorganisms is based on the following features:

Morphological:-shape, Gram stain, mobility, spore and capsule formation, dimensions;

2. Biochemical: type of metabolism, fermentation of sugars and polyhydric alcohols, proteolytic properties, etc.

3. Physiological: relation to sources of C, O, nitrogen, temperature, pH, humidity;

Cultural features: the nature of growth on solid and liquid media;

5. Molecular biological(features of the structure of DNA).

At present, the international taxonomy of bacteria according to Bergi is accepted. Bergi is an American scientist who led the school of microbiologists, who, under his leadership, compiled the systematics of prokaryotes. Its first edition ("Guide to the Systematics of Bacteria") was published in 1923, the ninth - I t in 1984, 2 t - in 1986, 3 t - in 1989.

According to this systematics, depending on the structure of the cell wall, all prokaryotes are divided into 4 sections:

Gracilicutes(gracilis - thin, slender, cutes - skin). All gram-negative microorganisms are included in the department.

2. Firmicutes- (firmis - strong, durable). The department includes gram-positive cocci, rods and filaments.

3. Tenericute s - (tenes - soft, gentle).

The division includes mycoplasmas, which lack a cell wall.

4. Mendosicutes(mendosi - imperfect cell wall). Microorganisms that do not contain murein and live in extreme conditions are included - methane-forming, sulfur-oxidizing, halophilic, thermoacidophilic, etc.

After the division are the following taxa: class, group(or section) order(suffix - ales), family(- ceae), genus, kind.

In microbiology, the binomial nomenclature proposed by K. Linnaeus is used: the first word means genus and is written with a capital letter, the second is the species name and is written with a small letter.

The name of the genus includes some morphological, physiological features or the surname of the author who studied this genus. The species name is a description of the colony (color, shape) or source of origin.

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The taxonomy of microorganisms is extremely complex. Many microorganisms have the same morphological features, but different physiological properties. The evolution of many microorganisms is unknown, and the relationships between them are often unclear. In addition, the concept of "species" for microorganisms still does not have a clear definition. Usually, microorganisms that have common morphological and physiological properties and are similar in antigenic structure are referred to one species.

In the environment, microorganisms that make up this type, cause similar processes as a result of their life. The name of the species in microorganisms is given according to the binomial (double) nomenclature proposed by Linnaeus in 1760.

1. Systematics of microorganisms.

The first word in the name of a microorganism means genus and is usually Latin, the second word is the specific name of the microbe. The genus name is written with a capital letter, and the species name is written with a lowercase letter, for example Bacillus anthracis - anthrax, the causative agent of anthrax.

When writing, the generic name of a bacterium is usually abbreviated to the initial letter, for example, E. coli (Escherichia coli) - Escherichia coli.

The names of the scientists who discovered them can be reflected in the name of microorganisms. Thus, Brucella was described by the English scientist Bruce, Giardia by the Russian doctor Lyamble. In honor of the American microbiologist Salmon, the genus Salmonella is named, the German scientist Escherich - the genus Escherichia, the Japanese microbiologist Shiga - the genus Shigella.

Sometimes the name of microorganisms is associated with the name of the organ they infect: for example, meningococci cause damage to the meninges, pneumococci cause damage to the lungs, etc. These names are not consistent with the rules of nomenclature.

Systematics of microorganisms

Systematics - the distribution of microorganisms in accordance with their origin and biological similarity. Systematics deals with a comprehensive description of the species of organisms, elucidating the degree of kinship between them and combining them into classification units of different levels of kinship - taxa.

The main issues addressed in taxonomy (three aspects, three pillars of taxonomy) are classification, identification and nomenclature. In other words, the main goal of taxonomy is to identify a microorganism. Classification is the distribution (unification) of organisms in accordance with their common properties (similar genotypic and phenotypic characters) among various taxa.

Taxonomy is the science of methods and principles of distribution (classification) of organisms in accordance with their hierarchy.

The following taxonomic units (taxa) are most often used - strain, species, genus. Subsequent larger taxa - family, order, class. In the modern view species in microbiology- a set of microorganisms that have a common evolutionary origin, a close genotype ( a high degree 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 compared features and mathematical consideration of the degree of correspondence.

A large number of compared phenotypic traits and the principle of their equal significance 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 mutual arrangement, structure.

2. Tinctorial - the attitude to various dyes (the nature of staining), primarily to Gram stain.

On this basis, all microorganisms are divided into gram-positive and gram-negative.

Morphological properties and attitude to Gram staining usually make it possible to attribute the studied microorganism to large taxa - a family, a genus.

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

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

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.

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. The ability to form spores, the nature of the dispute.

9. Sensitivity to bacteriophages, phage typing.

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

Protein spectrum (polypeptide profile).

12. Sensitivity to antibiotics and other drugs.

13. Genotypic (use of methods of genosystematics).

Classification of microorganisms

The classification of microorganisms (root taxon) is the distribution of microorganisms according to similar or hallmarks into ordered groups.
The classification of microorganisms is one of the most difficult branches of microbiology.

The more complete our knowledge of organisms, the more accurately we classify them.
Modern classification microorganisms is built on a hierarchical basis. Different levels of the hierarchy (taxonomic categories, series, ranks) have their own names (from highest to lowest): kingdom, department, class, order, family, genus, species.

It is accepted that any particular microorganism must consistently belong to all 7 categories.

kingdom (lat.

regnum) is a hierarchical level of scientific classification of microorganisms, the taxon of the highest level among the main ones. Historically, there are five kingdoms of living organisms: animals; plants; mushrooms; bacteria; viruses. Since 1977, two more kingdoms have been added to them: protists; archaea. Since 1998, one more thing has been distinguished: chromium.

Division (lat. dvisio) is one of the highest ranks of the taxonomic hierarchy in microbiology. In the hierarchy of taxonomic categories, the department is above the class and below the kingdom.
The names of the departments, like the names of other taxa, the rank of which is higher than the genus, are uninominal, that is, they consist of one word - a noun, or an adjective used as a noun, in the plural, written with capital letter.Class (lat.

classis) is one of the main ranks of hierarchical classification in biological systematics. In the hierarchy of systematic categories, class is below division and above order. The class names, like the names of other taxa higher than the genus, are uninomial. Order (Latin ordo) is one of the main ranks of the hierarchical classification. In the hierarchy of systematic categories, it is below the class and above the family. In bacteriology, the standardized ending -ales is used to name the orders.

Carl Linnaeus expressed the opinion that "order is a subdivision of classes, introduced in order not to distinguish between genera in a number greater than they can easily be perceived by the mind." family (lat.

familia) is one of the main ranks of the hierarchical classification in biological systematics. In the hierarchy of systematic categories, the family is lower than the order and higher than the genus. The names of families are formed according to the rules regulated by the International Code of Nomenclature for Bacteria. The name of the family is formed from the name of the type genus, to the base of which the standard ending aceae is added.

Genus (Latin genus) is one of the main ranks of hierarchical classification in biological systematics.
In the hierarchy of systematic categories, the genus is below the family and above the species. The scientific name of the genus is uninomial, that is, it consists of one word. The codes of biological nomenclature require that this word be Latin in form, that is, written in the letters of the Latin alphabet and subject to the rules of Latin grammar.

The genus name is treated as a noun in singular and is capitalized. There are no other restrictions, so the genus name can be either a word borrowed from classical Latin or a Latinized word from any language (most often from ancient Greek). Often the name of the genus is a word formed from a surname or a given name (for example, Escherichia) from the name of the scientist Escherich.

From the basis of the generic name, the names of the taxa of the family group are formed. The rules for the formation and use of generic names are established by the rules set forth in the International Code of Nomenclature for Bacteria. A species (lat. species) is a taxonomic, systematic unit, a group of individuals with common morphophysiological, biochemical and behavioral characteristics, capable of interbreeding, producing fertile offspring in a number of generations, regularly distributed within a certain area and similarly changing under the influence of environmental factors.

A species is a real-life unit of the living world, the main structural unit in the system of organisms. In the classification of microorganisms, the species problem is the most important and difficult. Without a species definition, it is impossible to build a classification.

A species is a set of microorganisms that have a common origin and genotype, similar morphological and biological properties.

The species of bacteria is determined by the sum of various features and properties and is a product of the evolution of living matter, which has its own history of development, formation and stabilization as a result of adaptation to the conditions of existence. A pure culture is a set of homogeneous microorganisms isolated on a nutrient medium, which are characterized by similar biological properties.

A strain is a pure culture of a microorganism isolated from a specific source and distinct from other members of the species.
A clone is a collection of offspring grown from a single microbial cell.

In modern classifications, any sign is used, as long as it stands out and makes it possible to recognize the microorganism under study. Relatively new is the concept of supra-kingdom, or biological domain.

It was proposed in 1990 by Carl Woese and introduced the division of the entire biomass of the Earth into three domains:
1) eukaryotes (a domain that unites all organisms whose cells contain a nucleus);
2) bacteria;
3) archaea.

Based on the structural features of microorganisms and other unicellular organisms, they are divided into two distinct groups: eukaryotes and prokaryotes.
Eukaryotes are higher microorganisms, or protists.

Their cells are structurally similar to plant and animal cells. Eukaryotes include algae, fungi and protozoa. Eukaryotic cells have a differentiated nucleus separated from the cytoplasm by a nuclear membrane. Inside the nucleus is a set of chromosomes, which, doubling in the process of division - mitosis, are transferred to daughter cells. In the cytoplasm of eukaryotes, there is a developed endoplasmic reticulum originating from the cytoplasmic membrane, as well as mitochondria and various organelles - plastids.

Prokaryotes are lower protists.

These include bacteria and blue-green algae. Prokaryotes differ sharply in their structure from all other living organisms. In the cell wall of prokaryotes, peptidoglycans (glycoproteins) were found that were not found in the composition of eukaryotic cells. The nucleus of a prokaryotic cell is not differentiated: deoxyribonucleic acid (DNA), which makes up the chromosome, is freely immersed in the cytoplasm, the nuclear membrane is absent. The endoplasmic reticulum is poorly developed, so the division into "compartments" in the cytoplasm is not pronounced.

Until now, there is no unified international classification of microorganisms. Mushrooms, protozoa and viruses have their own specific classification, which will be presented in the relevant sections.

There are also various classification schemes for bacteria and blue-green algae. Burgey's taxonomy, set out in the "Determinant of Bacteria", is gaining more and more recognition. last time published in 1974. It describes and systematizes more than 1500 species of microorganisms belonging to prokaryotes.

Microorganisms related to prokaryotes, in Bergey's definition, are divided into two sections: I - cyanobacteria (blue-green algae) and II - bacteria. The department of bacteria is described and systematized in the most detailed way. It includes, in addition to bacteria proper (cocci, bacilli, spirilla), microorganisms such as spirochetes, actinomycetes, rickettsia, chlamydia, mycoplasmas. The bacteria department is divided into 19 groups, or parts, which corresponds to subdivisions or subclasses.

These groups include orders, families, genera, and species that have great importance for a person. Among the microorganisms that cause human diseases are: spirochetes (group 5), gonococci, staphylococci, streptococci (groups 10 and 14), pathogens of intestinal infections, including cholera (group 8), pathogens of anaerobic infections and anthrax (group 15). ), actinomycetes and mycobacteria (group 17), rickettsia and chlamydia (group 18), mycoplasmas (group 19).

Microorganism identification

The main phenotypic and genotypic characteristics used for the classification of microorganisms are also used for identification, i.e. establishing their taxonomic position and, above all, their species affiliation is the most important aspect microbiological diagnosis of infectious diseases. Identification is carried out on the basis of studying the phenotypic and genotypic characteristics of the studied infectious agent and comparing them with the characteristics of known species.

In this work, reference strains of microorganisms, standard antigens and immune sera to known prototype microorganisms are often used. Pathogenic microorganisms often study morphological, tinctorial, cultural, biochemical and antigenic properties.

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 (with a lowercase letter). Examples are Shigella flexneri, Rickettsia sibirica.

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

In microbiology, there are also the concepts of "strain" and "clone".

Strain - microorganisms of the same species, isolated simultaneously from one source: from a patient or carrier, as well as from environmental objects (from water, food, household items). The strains differ from each other in individual characteristics, for example, resistance to antibiotics, sulfonamides, the ability to cause unequal severity, clinical course and outcome. infection. However, strains of one species have all the features that characterize them as a species.

They also retain their specific name, to which they add the initial letters of the surname or initials of the patients from whom the given strain was isolated, or the name of the territory in which it was found. For example, different strains of the influenza virus are named after the place of their isolation: the "Asian" strain of the influenza virus, the "Hong Kong" strain of the influenza virus.

Clone - a culture of microorganisms obtained by reproduction of one cell of a given species or strain.

The term "culture" or "population" is used to refer to a set of microbes growing on a nutrient medium from one or more cells of the same species (from the French population - population). A population of microbes consisting of individuals of the same species is called a pure culture, and of individuals different types- mixed culture.

The basic principle of bacteriological work is isolation and study of the properties of only pure(homogeneous, without admixture of foreign microflora) cultures.

1 2 3 4 5 6 7 8 9 10

Numerical (numerical) taxonomy is based on the use of the maximum number of compared features and mathematical consideration of the degree of correspondence. A large number of compared phenotypic traits and the principle of their equal significance made classification difficult.

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

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

2. Tinctorial - relation to various dyes (the nature of staining), primarily to Gram stain.

On this basis, all microorganisms are divided into gram positive and gram negative.

Morphological properties and attitude to Gram staining allow, as a rule, to attribute the studied microorganism to large taxa - a family, a genus.

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

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 food, type of breathing ( aerobes, microaerophiles, facultative anaerobes, strict anaerobes).

7.Mobility and types of movement.

8.Ability to sporulation, the nature of the dispute.

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 methods of genosystematics).

In recent decades, for the classification of microorganisms, in addition to their phenotypic characteristics (see paragraphs 1-12), various genetic methods are increasingly and effectively used (study of the 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, more often they proceed from the conditional assumption that the degree of homology of more than 60% (for some groups of microorganisms - 80%) indicates that microorganisms belong to the same species (different genotypes - one genospecies), 40-60% - to the same genus.

Identification.

The main phenotypic and genotypic characteristics used for the classification of microorganisms are also used for identification, i.e.

establishing their taxonomic position and, above all, their species, the most important aspect of the microbiological diagnosis of infectious diseases. Identification is carried out on the basis of studying the phenotypic and genotypic characteristics of the studied infectious agent and comparing them with the characteristics of known species.

Nomenclature- name of microorganisms in accordance with international rules.

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

Strain— any specific specimen (isolate) of a given species. Strains of the same species that differ in antigenic characteristics are called serotypes (serovariants) abbreviated serovars), by sensitivity to specific phages- fagotypes, biochemical properties - chemovars, according to biological properties - biovars etc.

The colony- a visible isolated structure during the reproduction of bacteria on dense nutrient media, it can develop from one or more parental cells. If the colony developed from one parent cell, then the offspring is called clone.

culture- the whole set of microorganisms of the same species grown on a solid or liquid nutrient medium.

The basic principle of bacteriological work is isolation and study of the properties of only pure(homogeneous, without admixture of foreign microflora) cultures.

Morphology of bacteria.

Prokaryotes differ from eukaryotes in a number of key ways..

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

2. The absence of a developed endoplasmic reticulum, the Golgi apparatus.

3. Absence of mitochondria, chloroplasts, lysosomes.

4. Inability to endocytosis (capture of food particles).

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

Significantly smaller sizes (as a rule). Most of the bacteria have a size of 0.5-0.8 micrometers ( micron) x 2-3 µm.

According to the form, the following main groups of microorganisms are distinguished.

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

2. Rod-shaped.

3.Corrected.

4. Filiform.

coccoid bacteria (cocci)according to the nature of the relationship after division, they are divided into a number of options.

1.micrococci.

Cells are located alone. They are part of the normal microflora, are in the external environment. They do not cause disease 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. The division is carried out in one plane, the multiplying cells keep the connection (do not diverge), forming chains.

Many pathogenic microorganisms are the causative agents of tonsillitis, scarlet fever, purulent inflammatory processes.

4.Tetracocci. Division in two mutually perpendicular planes with the formation of tetrads (i.e., four cells each). 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 lat. - a bunch of grapes). They divide randomly in different planes, forming clusters resembling bunches of grapes.

They cause numerous diseases, primarily purulent-inflammatory.

rod-shaped microorganisms.

1. Bacteria are rods that do not form spores.

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

3. Clostridia - anaerobic spore-forming microbes. The diameter of the spore is greater than the diameter (diameter) of the vegetative cell, and therefore the cell resembles a spindle or a tennis racket.

It must be borne 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.

Convolute forms of microorganisms.

1. Vibrio and campylobacter - have one bend, can be in the form of a comma, a short curl.

2.Spirilli - have 2-3 curls.

3. Spirochetes - have a different number of curls, axostyle - a collection of fibrils, a specific character of movement for various representatives and structural features (especially the end sections).

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, a more detailed description of vibrios and spirochetes will be given in the relevant sections of private microbiology.

We complete this section brief description(key) to characterize the main genera of microorganisms of medical importance, based on the criteria used in the Berge Bacteria Key.

Key to major groups of bacteria

The main groups of bacteria | genera of bacteria

1. Bending bacteria with thin walls, mobile

nost is provided due to sliding - gliding-

living bacteria

2. Bending bacteria with thin walls, mobile - Treponema

ness is associated with the presence of an axial thread spirochetes Borrelia, Leptospira

3. Rigid bacteria with thick walls, motionless

nye or mobile due to flagella - eubacteria

Mycelial forms of Mycobacterium, Actino-

myces, Nocardia, Strep-

B. Simple unicellular

2/ free-living

gram positive:

cocci Streptococcus, Staphy-

non-spore-forming rods Corynebacterium, Lis-

teria, Erysipelothrix

spore-forming rods

including obligatory aerobes Bacillus

including obligatory Clostridium anaerobes

b. gram negative:

cocci Neisseria

non-intestinal coli

spiral shape Spirillum

including straight, very small sticks Pasteurella, Brucella,

Yersinia Francisella,

Haemophilus, Borde-

coli

including facultative anaerobes Escherichia, Salmone-

lla, Shigella, Klebsiel-

la, Proteus, Vibrio

including obligate aerobes Pseudomonas

including obligate anaerobes Bacteroides, Fuso-

4. Without cell walls Mycoplasma, Urea-

3. Structure of a bacterial cell.

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

Optional(minor) structural elements are Key words: cell wall, 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.

Systematics and classification of microorganisms

Consists of a double-stranded strand of DNA. The nucleoid is not separated from the cytoplasm by a nuclear membrane.

2.Cytoplasm- a complex colloidal system containing various inclusions of metabolic origin (granules 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, formation of the intercellular septum during division).

3.cytoplasmic membrane limits the cytoplasm from the outside, has a three-layer structure and performs a number of important functions - barrier (creates and maintains osmotic pressure), energy (contains many enzymatic respiratory systems, redox, carries out the transfer of electrons), 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, first of all, it provides mechanical protection and a permanent shape of cells; 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 for bacteria - peptidoglycan(mureic acids). An important feature of bacteria for taxonomy 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 retains the iodine complex after Gram staining. gentian violet(stained blue-violet), gram-negative bacteria lose this complex and the corresponding color after treatment and are stained pink by staining with fuchsin.

Features of the cell wall of gram-positive bacteria.

Powerful, thick, uncomplicatedly organized cell wall, which is dominated by peptidoglycan and teichoic acids, no lipopolysaccharides (LPS), 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, contains LPS, lipoproteins, phospholipids, diaminopimelic acid.

It is more complicated - there is an outer membrane, so the cell wall is three-layered.

When processing gram-positive bacteria with enzymes that destroy peptidoglycan, there are structures completely devoid of a cell wall - protoplasts.

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 adverse conditions of existence. As a result of a change in antigenic properties (loss of O- and K-antigens), a decrease in virulence and other factors, L-forms acquire the ability to stay for a long time ( persist) in the host organism, maintaining a sluggish infectious process.

The loss of the cell wall renders the L-forms insensitive to antibiotics, antibodies, and various chemotherapeutic agents whose point of application is the bacterial cell wall.

Unstable L-shape 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 them into classical forms of bacteria are genetically fixed.

In a number of ways, they are very similar to mycoplasmas and other mollicutes- bacteria in which the cell wall is absent as a taxonomic feature. Microorganisms related to mycoplasmas, 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 a cell wall), include capsule, flagella, microvilli.

Capsule or mucous layer surrounds the shell of a number of bacteria.

Allocate microcapsule, detected at electron microscopy in the form of a layer of microfibrils, and macrocapsule detected 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. At saprophytes capsules are formed in the external environment, in pathogens, more often in the host organism. 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 Guinsu), less often - from polypeptides.

Flagella. Motile bacteria can be gliding (moving on a solid surface as a result of wave-like contractions) or floating, moving due to filamentous spirally bent protein ( flagellic according to the chemical composition) formations - flagella.

According to the location and number of flagella, a number of forms of bacteria are distinguished.

1. Monotrichous - have one polar flagellum.

2. Lofotrichous - have a polar bundle of flagella.

3. Amphitrichous - have flagella at diametrically opposite poles.

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

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

Fimbriae or cilia- short threads 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, the fimbriae are adhesion and colonization factors.

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

Endospores and sporulation.

sporulation- a way to preserve certain types of bacteria in adverse conditions environment.

Endospores are formed in the cytoplasm, are cells with low metabolic activity and high resistance ( resistance) to drying, the action of chemical factors, high temperature and other adverse environmental factors. Light microscopy is often used to detect spores. according to Orzeshko. High resistance is associated with a high content calcium salt of dipicolinic acid in the spore shell.

The location and size of spores in different microorganisms is different, which has a differential diagnostic (taxonomic) value. The main phases of the “life cycle” of spores sporulation(includes the preparatory stage, the prespore stage, the formation of the shell, maturation and dormancy) and germination ending with the formation of a vegetative form. The process of sporulation is genetically determined.

Uncultivated forms of bacteria.

Many species of gram-negative bacteria that do not form spores have a special adaptive state - uncultivated forms.

They have low metabolic activity and do not actively multiply; do not form colonies on dense nutrient media, are not detected during crops. They are highly resistant and can remain viable for several years. Not detected by classical bacteriological methods, detected only by genetic methods ( polymerase chain reaction - PCR).

Principles of taxonomy of bacteria. Systematization, i.e., ordering of ideas about any objects, groups of living beings, including microorganisms, is necessary to facilitate the recognition of these objects, to establish the degree of relationship or physiological similarity between individuals or groups of individuals. Systematization of knowledge about microorganisms greatly facilitates practical work with them.

However, there is no sufficiently scientifically based classification system for bacteria (taking into account family ties within the group and between groups of microorganisms). This is explained by the difficulties in studying external features and physiological properties that often change under different living conditions; insufficiently reliable methods for establishing the degree of relationship and the lack of clear ideas about the evolutionary development of microorganisms in general.

The most modern classification system for bacteria is the International Burgey Classification. In 1974, the eighth edition was published, in the preparation of which 131 authors from 15 countries took part.

The systematic categories in this classification are kingdom, department, group, family, genus, species. All bacteria are assigned to the kingdom Procaryotae (organisms that do not have a differentiated nucleus), which is divided into two divisions.

The second section contains all bacteria of interest for technical and food microbiology. They are divided into 19 groups. The most important families are described in groups: 3, 7, 8,9, 14, 15, 16. This classification system has been constantly improved since its first edition in 1923. The introduction to the eighth edition of Burgey's guide indicates that there will be further its improvement and regrouping of systematic units is carried out.

IN practical work still use the foundations of the first scientific classification, created in 1896 by K. Lehman and R. Neumann. Taking into account the changes made to it over the past time, all bacteria are divided into three families - rod-shaped, spherical and convoluted.

Since many very diverse organisms are combined into each family, families are divided into genera. So, the family of spherical bacteria, depending on the nature of the association of cells into groups, is divided into genera: micrococci, streptococci, sarcin.

In certain sections of microbiology, for example, in medicine, there are also genera of diplococci and tetracocci.

The family of rod-shaped bacteria is divided into three genera: the genus of bacteria proper, which includes all those incapable of forming spores; a genus of bacilli that combines aerobic forms that are capable of forming spores; genus Clostridia, which includes anaerobic rod-shaped spore forms.

The family of convoluted bacteria, depending on the degree of tortuosity, is usually divided into the genus Vibrio (bacteria curved in the form of a comma), the genus Spirilla (large, gently convoluted), the genus Spirochaetes (thin, highly convoluted cells).

The division into genera is not enough for orientation in the properties of bacteria, since it is based only on external signs. Each genus combines bacteria that are similar in appearance, but often have completely different physiological characteristics and properties. Thus, in the genus of bacteria, the causative agent of putrefactive processes, the hay bacillus, the causative agents of fermentation of milk, the bulgarian stick, and others, and the causative agents of food infections, typhoid bacillus, dysentery, are combined. Therefore, genera are divided into species.

When determining the type of bacteria, in addition to morphological features (mobility, attitude to diagnostic stains, etc.), physiological (oxygen demand, ability to use various sugars, etc.) and cultural (the nature of the formed colonies, growth characteristics on some nutrient media, etc.). The name of a species of bacteria, as a rule, consists of two words, the first of which indicates belonging to the genus, and the second directly indicates the species. The generic name is written with a capital letter, the specific name is written with a lowercase letter. So, the name Bact. fluorescens refers to rod-shaped non-spore-forming bacteria (a genus of bacteria) that form the pigment fluorescein (a species - fluorescence).

Principles of taxonomy and classification of bacteria.

Systematics deals with the description of species of organisms, determining the degree of relationship between them and combining them into classification units (taxa). Classification is an integral part of systematics. It is reduced to the distribution of organisms in accordance with their characteristics among various taxa. Taxonomy- the science of the principles and methods of distribution (classification) of organisms in a hierarchical plan. The basic taxonomic unit in biology is the species.

Large taxonomic units: genus, family, order, class. Additional categories: subgenus, subtype, suborder, subclass.

A species is a group of closely related organisms that have a common root of origin, at this stage of evolution, are characterized by certain morphological, biochemical and physiological characteristics, separate selection from other species and are adapted to a specific habitat.

The specific features of microorganisms, a number of features and properties are used to classify them:

1. Morphological features - the size, shape and nature of the relative position.

2. Tinctorial properties - the ability to stain with various dyes. An important feature is the attitude towards Gram stain, which depends on the structure and chemical composition of the cell wall. With the destruction of the cell wall or loss (in the case of L-transformation), they become gram-negative. On this basis, all bacteria are divided into gram-negative (stained red) and gram-positive (stained purple).

3 Cultural properties- features of bacterial growth on liquid and complete nutrient media. Growth on liquid media with the formation of a film, sediment, turbidity.

Growth on dense nutrient media in the form of colonies, it seems possible to determine: the shape, size, edges of the colonies, surface, transparency and other properties.

In microbiology, special terms are used:

Ø The colony– visible with a simple eye an isolated structure resulting from the reproduction and accumulation of bacteria over a certain period of incubation.

Ø Incubation period- growth time of bacteria.

A colony is formed from one parent cell or several identical cells. A pure culture of the pathogen can be obtained by reseeding from an isolated colony.

Ø culture- The whole set of bacteria grown on a dense or liquid nutrient medium.

Ø Pure culture of the pathogen- one type of bacteria grown on a dense nutrient medium. In order to avoid diagnostic errors in bacteriology, only pure homogeneous cultures are studied.

Ø Strain is a specific specimen of this species.

4. Mobility of bacteria - distinguish between mobile and motionless. Mobile are divided into crawling or sliding, floating, moving in waves.

5. Sporulation - The shape and nature of the arrangement of spores in the cell.

6. Physiological properties - ways of feeding, type of breathing, growth and reproduction.

7.Biochemical properties - the ability to ferment (break down) carbohydrates, proteolytic activity, the formation of indole, hydrogen sulfide.

8. Genosystems - Study of the nucleotide composition of DNA and characteristics of the genome. The exact method of establishing the genetic relationship between bacteria is to determine degree of DNA homology. The more identical genes, the higher the degree of DNA homology and the closer the genetic relationship. DNA-DNA Molecular Hybridization Method used for taxonomy of bacteria. If the range of DNA homology from 60 to 100% determines belonging to the same species, the degree of homology from 40 to 60% - to different genera.

Currently, there is no universal, only correct classification. Depending on the task, microorganisms can be classified by morphological features (rods, cocci, convoluted, etc.), by tinctorial features (gram-positive, gram-negative, etc.), by physiological features (thermophilic, psychrophilic, acidophilic, aerobic etc.), by ecological traits (nitrogen-fixing, nitrifying, sulfate-reducing, cellulose-destroying, etc.), by interspecific relationships (antagonists, synergists, commensals, etc.), by types of taxis, genotypic and phylogenetic characters. Microorganisms are also classified according to the degree of danger to humans, animals and the environment. Thus, the classification of microorganisms is a subjective processing of objective characteristics.

Modern taxonomy of microorganisms includes three main areas:

1. Characterization of microorganisms- Obtaining all kinds of information about the properties and parameters necessary to assign the determined microorganisms to a particular taxon.

2. Classification or taxonomy, i.e. the process of ordering microorganisms into taxonomic groups based on similarity.

3. Nomenclature- assignment of scientific names to taxonomic groups (taxa).

The basic taxonomic unit in the taxonomy of microorganisms is view. According to general biological concepts, a species is a group of closely related organisms that have a common root of origin and at this stage of evolution are characterized by certain morphological, biochemical and physiological features, isolated by selection from other species and adapted to a specific habitat. An important species trait is the ability of organisms to interbreed and produce offspring.

The definition of a species in bacteria is fundamentally different from the classical definition of a biological species, since they do not have a sexual mode of reproduction. According to modern concepts, closely related organisms, with a 70% level of DNA homology and similar in terms of morphological, biochemical, and physiological characteristics, are classified as one type of bacteria.

The following taxonomic categories are also used in the hierarchical classification of microorganisms: subspecies- a group of closely related similar organisms within kind with a level of DNA homology above 70%; genus- a taxonomic group that unites related species, and further - family, suborder, order, subclass, class, realm And domain(or supra-kingdom). Families and domains are now largely described, while other taxonomic groups are in the process of systematization.

Domains are the highest taxa of microorganisms, corresponding to previously identified kingdoms. According to the modern classification, the entire diversity of microorganisms is represented by three domains: Bacteria (prokaryotic microorganisms, true bacteria), Archaea (another evolutionary branch of prokaryotic microorganisms) and Eukarya (eukaryotic microorganisms)(Fig. 2). Of these, two domains (Bacteria and Archaea) include only representatives of prokaryotes, which are separated into a separate supra-kingdom - Procariolae.

Fig.2. Universal phylogenetic tree of living organisms.

The most accurate, informative, and user-friendly classification system is one in which taxa are defined based on a variety of consistent characteristics obtained using various modern methods. Such an approach to the selection of taxa is called polyphasic.

The main methods of modern polyphasic taxonomy are: genotypic, phenotypic and phylogenetic.

The genotypic method is dominant in polyphasic taxonomy. It is based on the study of the C+G composition of DNA, on the study of DNA-rRNA homology, on the establishment of related relationships between microorganisms that are encoded in the nucleotide sequences of the 16S or 23S r-RNA genes. For example, when determining the belonging of a microorganism to a certain species, the level of similarity of the DNA nucleotide sequences of about 70% plays a paramount role. Therefore, the genotypic method is often called the method of genomic fingerprinting.

Phenotypic studies are used most often in various schemes for the identification of microorganisms, for the formal description of a taxon, from variety and subspecies to genus and family. While genotypic data is necessary to place a taxon on a phylogenetic tree and in a classification system, phenotypic characterization provides descriptive information that allows identification of a particular microorganism species. Classical phenotypic characteristics include morphological, physiological, biochemical, chemotaxonomic and serological characteristics of microorganisms.

Morphological features indicate the size and shape of the microorganism (coccus, bacillus, spirilla), whether it has a capsule or spores, whether the cells are combined into chains, tetrads or packages, whether they have flagella and how they are located, whether the cells are stained according to Gram. The morphology of bacteria includes the study of cultural properties, i.e. the nature of growth on nutrient media, the shape of colonies on dense nutrient media, pigment formation.

Physiological features characterize the mechanism of metabolism, the method of obtaining energy, the ability of a given microorganism to transform certain substances, its relationship to carbon, nitrogen, oxygen, temperature, pH of the environment.

Biochemical signs are determined by the ability of microorganisms to decompose certain sugars, form hydrogen sulfide, ammonia and other compounds.

Chemotaxonomic features characterize the chemical composition of the cell cytoplasm. The taxonomic specificity of the composition of fatty acids, lipoproteins, lipopolysaccharides, pigments, polyamines, proteins and other chemical components of the cell is widely used in the classification of microorganisms.

Serological properties, or serotyping, are based on the detection of variability in the antigenic components of bacterial cells. Such components can be flagella, fimbriae. capsules, cell wall, enzymes and toxins. To identify the antigenic properties of a bacterial cell, various serological reactions are used: precipitation reaction, complement bonding reaction, precipitation, etc.

Thus, phenotypic characteristics are distinguished by a large volume and variety of information obtained, which is difficult to process manually. There was a need for a computer, numerical analysis of the data obtained. Numerical (numerical) taxonomy has appeared, which allows using computer programs to analyze the phenotypic and genotypic characteristics of microorganisms. The use of numerical analysis in taxonomic practice is called "computer identification".

Phylogenetic methods (from the Greek phylon - genus, tribe and genesis - origin, occurrence) allow us to trace the process of historical development of microorganisms both in general and their individual taxonomic groups: species, subspecies, genera, families, suborders, orders, subclasses, classes , kingdoms and domains.

Phylogenetic relationships between microorganisms are studied by the methods of genomic fingerprinting, molecular biology, and computer identification. Based on the obtained data, phylogenetic trees are built, which reflect the evolutionary relationships between microorganisms (Fig. 3). The created phylogenetic trees cannot be used to build a hierarchical classification of microorganisms and do not replace taxonomy. They are one of its elements.

Nomenclature- deals with issues of precise and uniform names. Ego is a system of names used in a certain field of knowledge. In accordance with international rules, taxonomic groups of microorganisms are assigned names.

Even before the introduction of the first rules of nomenclature, a huge number of microorganisms were described. Moreover, the same bacterium could be assigned to taxa with different names. To avoid this, the International Code of Nomenclature defined all the priority names of bacteria published since May 1, 1753. As a result, a "List of Recognized Names of Bacteria" was created, which came into force on January 1, 1980. Currently, the name of microorganisms is assigned in accordance with the rules of the International Code of Nomenclature for Bacteria. The competence of the Code extends only to the rules for assigning and using the scientific names of microorganisms. Classification issues are resolved regardless of the Code on the basis of ongoing taxonomic studies.

Rice. 3. Phylogenetic tree of bacteria.

In microbiology, as in biology, a double (binary) nomenclature, proposed as early as 1760 by Carl Linnaeus, is adopted to designate bacterial species.

The first word is the genus name. Usually this is a Latin word, it is written with a capital letter and characterizes any morphological or physiological feature, or the name of the scientist who discovered this microbe. For example, the genus Pasteurella is named after the French scientist L. Pasteur, the American microbiologist Salmon - the genus Salmonella, the German scientist T. Escherich - the genus Escherichia, the Japanese microbiologist Shiga - the genus Shigella, the English bacteriologists D. Bruce and S. Erwin - the genera "Brucella" and "Ervinia", Russian scientists Kuznetsov and Lyambl - the genera "Kuznetsovia" and "Lamblia", etc. The genus name of a microorganism is usually abbreviated to one or two letters.

The second word denotes the specific epithet in the name of the microorganism and, as a rule, is a derivative of a noun that describes the color of the colony, the source of origin of the microorganism, the process or disease caused by it. The species name is capitalized and never abbreviated. For example, Escherichia coli means that Escherichia live in the intestines, Pasterella pestis means pasteurella that causes plague, Bordetetia pertussis means bordetella that causes cough, Clostridium tetani means clostridium that causes tetanus, etc.

S.N. Vinogradsky and M. Beijerinck, taking into account the diversity of bacterial metabolism, suggested that the genus name reflect the characters associated with the morphology, ecology, biochemistry and physiology of microorganisms. This is how the names that are the key to the characterization of the microorganism appeared: Acetobacter (acid-forming bacteria), Nitrosomonas (nitrifying bacteria), Azotobacter (bacteria that fix atmospheric nitrogen), Chromobacterium (pigmented bacteria), B. stearothermophiliis (wax heat-loving bacteria), etc.

Sometimes, as an integral part of taxonomy, identification(definition) of microorganisms. However, this is not entirely correct, since identification uses already built classification systems and specific characteristics of microorganisms indicated in the identification keys (tables). Microorganism identification schemes are a kind of test of the quality of the classification system. For the identification of microorganisms, phenotypic and genotypic methods, methods of computer identification analysis and genomic fingerprinting are widely used.

In 1923, D. Bergey released the first international bacterial determinant. Subsequent editions have been prepared by the International Committee on Systematics of Bacteria. The ninth, last American edition of Bergey's Manual of Determinative Bacteriology, was published in 1994. The abbreviated name of the Guide is BMDB-9. In Russian translation, BMDB-9 was published in 1997. It introduces the diversity prokaryotes and takes a step towards attempts to identify microorganisms isolated from the environment.

According to BMDB-9, bacteria are classified (based on phenotypic traits) into four main categories:

1. Gram-negative eubacteria with cell walls.

2. Gram-positive eubacteria with cell walls.

3. Eubageria, devoid of cell walls.

4. Archaebacteria.

The main object in the identification of microorganisms is a pure culture of an isolated bacterium, called a "strain" or "clone".

Strain(from German stammen - to occur) is a bacterial culture of the same species, isolated from different objects or from the same object at different times, and differing in minor changes in properties (for example, in sensitivity to antibiotics, enzymatic activity, ability to form toxins ). Typically, strains of one species are adapted to a particular habitat.

under the term " bacterial culture» understand the population of microbial cells at a given place and at a given time. These can be microorganisms grown on a solid or liquid nutrient medium in a laboratory. A culture of microorganisms grown on a solid or liquid nutrient medium from individuals of the same species by successive subcultures of a single colony is called clean.

Pure bacterial cultures obtained from a single original cell are called clones(from Greek klon - offspring). A clone is a genetically homogeneous population.

A mixed culture is called a culture of heterogeneous microorganisms isolated from the material under study, for example, from water, soil, air.