MICROBIOLOGY - M.H. Serhiichuk - 2008

Chapter 8. MICROORGANISMS AND THE ENVIRONMENT

Interactions of Microorganisms in Nature

During evolution, every group of organisms had to adapt not only to abiotic environmental conditions (the habitat) but also to other living organisms. Adaptation through prolonged, close coexistence between different organisms led to the acquisition of new metabolic traits, enabling them either to benefit from this association or to withstand mutual competition. This phenomenon of organisms coexisting is known as Symbiosis (from Greek symbiosis – living together).

Symbiotic associations formed by microorganisms with plants, animals, and other microorganisms are categorized based on their degree of intimacy into ectosymbiosis and endosymbiosis. In ectosymbiosis, microorganisms maintain an external position relative to their host, whereas in endosymbiosis, the microorganism develops inside the host Cell.

Depending on the effect symbionts have on each other, interactions can be viewed as positive or negative. Positive interactions include:

- mutualism (from Latin mutuus – reciprocal): a form of symbiosis where both partners benefit from their coexistence. Often, this relationship is obligate (inseparable);

- syntrophy (from Greek syn – together, trophe – nourishment): the growth of one or more microbial species on a medium that is individually inaccessible to each of them separately;

- commensalism (from Latin com – together, mensa – table, meal): a form of symbiosis where one partner relies on the other to regulate its relationship with the environment. The existence of the commensal remains unnoticed by the host, representing a unidirectional syntrophy;

- synergism: a form of coexistence where associates experience an enhancement of their physiological functions.

Negative interactions involve competition (from Latin concurrere – to clash) or antagonism (from Greek antagonisma – dispute, struggle). Competition can be passive (different organisms utilize identical nutrients; fast-growing forms have the advantage) or active (driven by The production of bactericidal substances). A harsh example of competitive interaction is parasitism (from Greek parasitos – parasite, sponger), where one symbiont uses another as a habitat, and predation, where one uses another as food.

Natural interactions between various organisms are so complex and multifaceted that they quite often cannot be assigned to any single specific type.

Microbial interactions. Unlike laboratory conditions, where pure cultures are artificially maintained for microorganisms, in nature Bacteria are forced to endure the Struggle for Existence. Non-competitive microorganisms will inevitably disappear from the community.

In passive antagonism, one microorganism is displaced by another if the population growth of both species is limited by the same vital resource, the quantity and/or availability of which is restricted. For instance, when tubercle bacteria and saprophytic microflora are cultivated on an artificial nutrient medium, Saprophytes generally predominate due to their faster growth rate. Experiments have proven that altering experimental conditions can reverse the outcome of competitive interactions, which in many cases may realistically reflect seasonal changes. For example, during the co-cultivation of Spirillum sp. and Pseudomonas sp. at temperatures of 16^о C and above, Spirillum sp. held the advantage, whereas when the Temperature was lowered to 2^о C on the same substrate, Pseudomonas sp. developed more rapidly.

Active antagonism is caused by the secretion of bactericidal substances. These substances can be non-specific metabolic products (organic acids, alcohols, ammonia, phenols, hydrogen peroxide, etc.) or specific ones (Antibiotics).

Metabolic products such as acids and alcohols are toxic to any cell. Thus, when bacterial populations develop in milk, an independent growth of various microbial species is initially observed. However, in the presence of lactic acid bacteria, the milk gradually becomes acidic, leaving acid-tolerant lactic acid cocci and rods with the advantage. Over time, lactic acid rods, being more acid-tolerant, eventually displace the cocci as well.

Acetic acid bacteria can be maintained in pure culture without taking special precautions against contamination. The high concentration of acetic acid in the medium prevents the proliferation of other microorganisms.

Ureolytic bacteria facilitate the accumulation of ammonia during urea Hydrolysis, which renders the medium strongly alkaline. High alkalinity and a high concentration of ammonia in the environment prevent the growth of other microorganisms.

The action of specific metabolic products (antibiotics) aims to inhibit microorganisms sensitive to them. However, there is no definitive consensus regarding the Biological Significance of antibiotics for the microorganisms themselves. Under natural conditions, antibiotics generally cannot accumulate in sufficient quantities to exert a neutralizing effect on other microorganisms. For example, Streptomyces olivocinereus, a heliomycin producer, inhibits the population of Arthrobacter crystallopoietes in non-sterile soil, but this inhibitory effect is observed only at a producer density of at least 10⁶ colony-forming units per 1 g of soil. In another experiment, Escherichia coli and an antibiotic-producing streptomycete that inhibits E. coli growth were cultivated simultaneously. During their joint cultivation, antibiotic-resistant mutants of Escherichia coli emerged. Over time, the fast-growing E. coli completely displaced the slower-growing streptomycete Cells.

It is hypothesized that certain antibiotics may regulate specific processes within their producers. For instance, the synthesis of Polypeptide antibiotics by endospore-forming bacteria coincides with intensive sporulation. Antibiotics are also viewed as accidental metabolic by-products of no significance to the organisms that produce them. Although the question of the Biological Role of antibiotics remains unresolved, in some cases it has been shown that their accumulation AIDS microbial survival in the natural environment.

Competition manifests most vividly in the forms of parasitism and predation. Drawing a clear boundary between these types of interactions is difficult because both parasites and predators satisfy their nutritional needs at the expense of a victim. The difference lies in the fact that predators kill their prey relatively quickly, whereas parasites feed on a living Organism over a sustained period.

Microbial parasitism on other microorganisms is relatively rare. For instance, Vampirovibrio chlorellavorus is an obligate parasite of the unicellular alga Chlorella. This vibrio is incapable of growing on organic media or even on dead Chlorella cells. The bacteria attach to the algal Cell wall; several dozen vibrios may attach to a single cell. Attached vibrios increase the permeability of the algal cell wall and grow by utilizing nutrients entering its cell. Eventually, the algal cell stops growing and dies. However, antibiotics such as penicillin can kill the parasitic bacteria without harming the alga. Cured Chlorella cells are capable of resuming normal development.

Another vibrio (Bdellovibrio) can be regarded as a true predator. Cells of Bdellovibrio can attach to other Bacterial cells and penetrate them. Once inside, the predator grows by utilizing the Contents of the host cell as a nutrient substrate and then divides. Over time, the host cell lyses, and the predator searches for a new victim. The range of potential prey is quite broad, though it most frequently comprises enteric bacteria.

Positive interactions between different microbial species can be characterized as syntrophy. Syntrophy is the ability of two or more bacterial species to jointly carry out a process that neither of them could accomplish independently. The basis of such interactions may include The transfer of growth factors, the production by one organism of a substrate suitable for The Development of another, or the removal by one organism of products toxic to another. Several mechanisms may operate simultaneously.

Syntrophy based on substrate exchange is observed, for example, when microorganisms degrade Cellulose in a medium lacking combined nitrogen. Cellulose-degrading bacteria are incapable of MOLECULAR Nitrogen Fixation. They receive nitrogen fixation products from nitrogen-fixing bacteria. At the same time, nitrogen-fixing bacteria cannot use cellulose as a source of energy and carbon; instead, they utilize the hydrolysis products derived from cellulose-degrading bacteria. For this community, developing under aerobic conditions, the consumption of oxygen by cellulose-acting aerobes is also crucial, as a reduced oxygen level in the medium is favorable for nitrogen fixation.

Syntrophy, based on the removal of toxic metabolic by-products from the environment, can be observed in associations involved in methane oxidation. Methylotrophic bacteria possess a low-Specificity monooxygenase that, alongside methane, partially oxidizes other higher Hydrocarbons, resulting in The formation of products highly toxic to the methylotrophs. If methylotrophs thrive in associations with microorganisms capable of oxidizing these toxic compounds, methane-oxidizing associations remain stable, whereas pure cultures may rapidly die out.

In some cases, symbiotic relationships lead to the formation of a consortium (from Latin consortium — partnership, community), in which cells of two different species are united almost as a single organism. Such a consortium is formed by bacteria of the genus Desulfotomaculum and cells of Chlorobium phaeobacteroidus. Sulfate-reducing Desulfotomaculum bacteria occupy the center of the association, while photosynthetic sulfur bacteria reside On the surface. Thriving in the illuminated zone of Water bodies under anaerobic conditions, the photosynthetic bacteria supply the sulfate reducers with Organic compounds and oxidized sulfur, while Desulfotomaculum releases hydrogen sulfide and provides the photosynthetic bacteria with a reducing agent. As a result of this interaction, the consortium can develop in aquatic environments where only traces of hydrogen sulfide are present in the anaerobic zone. The consortium exhibits both photo- and chemotaxis. Division of the organisms comprising the consortium occurs synchronously, indicating a high degree of integration.

If the presence of a symbiont is essential for only one of the partners, it is referred to commutation or commensalism. For instance, microorganisms incapable of synthesizing cyanocobalamin on their own, but requiring it for growth, can develop around colonies of microorganisms actively synthesizing this vitamin. The existence of the symbiont goes unnoticed by the vitamin-producing microorganism. Another example is The breakdown of penicillin by penicillinase from aerobic spore-forming bacteria, which enables penicillin-sensitive microorganisms to grow.

The mechanisms of bacterial "mutual aid" are not restricted solely to Nutrition. For instance, the human pathogens Veillonella parvula and Actinomyces viscosus, which are non-motile, attach themselves in the Oral Cavity to The surface of normal oral microflora capable of gliding motility, thereby being transported to microenvironments favorable for their development.

The phenomenon of synergism (where associates exhibit enhanced physiological functions) has found application in BIOTECHNOLOGY FOR THE microbiological synthesis of biologically active compounds. Co-cultivation of two actinomycete cultures — Streptomyces noursei (a protease producer) and S. violocinereus (which does not synthesize Enzymes) — results in a sixfold increase in enzyme yield. It turned out that S. violocinereus produces a stimulator that affects the Development of the enzyme producer.

Other Examples of syntrophic relationships include polymicrobial infections, such as gas gangrene, caused by the combined action of several species of the genus Clostridium in association with staphylococci and streptococci.

Thus, dynamic relationships that often lack distinct boundaries are established among microorganisms in natural associations. The factors promoting specific forms of interaction are determined by concrete environmental conditions as well as the metabolic CHARACTERISTICS OF THE microorganisms themselves.

Interactions between microorganisms and plants. Microorganisms form a wide range of symbiotic associations with higher plants

As ectosymbionts or epiphytes (from Greek epi — upon, phyton — plant), they colonize the leaf surface — the phyllosphere (from Greek phyllon — leaf, sphaire — sphere, ball), and the soil directly surrounding plant roots — the rhizosphere (from Greek rhiza — ROOT). As endosymbionts, microorganisms penetrate the root Tissues and form mycorrhizae (when Fungi are involved) or nodules (upon bacterial invasion).

Microorganisms inhabiting the plant phyllosphere not only reside on the leaf surface but also actively proliferate there. The development of the phyllosphere is sustained by nutrients leached from leaves by water. Dew and leaf washings contain Amino Acids, CARBOHYDRATES, hydrocarbons, organic acids, phytohormones, and Inorganic Compounds. Nutrients may also originate from dust particles settling on the foliage.

The taxonomic COMPOSITION OF THE phyllosphere is quite diverse. Although certain species may predominate on specific plants, strict phyllosphere specificity has not been proven. Up to 80% of the total epiphyte population consists of Erwinia herbicola cells. Certain lactic acid bacteria, such as Lactobacillus plantarum, are also encountered. Bacteria capable of molecular nitrogen fixation are consistently detected and play a significant role in nitrogen accumulation; approximately 15% of total molecular nitrogen is fixed within the phyllosphere. Bacilli and actinomycetes are sparse, whereas fungal spores and germlings (Penicillium, Fusarium, Mucor, etc.) are more frequently found. A characteristic feature of most phyllosphere bacteria is their ability to produce melanin and/or carotenoid pigments, which shield the cells from the detrimental effects of solar radiation. The synthesis of extracellular Polysaccharides protects microbial cells against both radiation and desiccation. Furthermore, this mucilage enhances Cell Adhesion, preventing the bacteria from being washed off the leaves even during heavy rainfall.

In addition to obtaining nutrients from plants, epiphyte microorganisms produce substances that plants can utilize as growth stimulants. However, the phyllosphere may also harbor phytopathogenic microorganisms capable of inducing plant diseases under favorable conditions.

The plant root system is invariably densely populated with bacteria. Microorganisms are located directly on the root surface as well as in the surrounding rhizosphere soil. The bacterial population in the rhizosphere is 10 to 100 times greater than that in root-free soil.

The enhanced proliferation of bacteria in the rhizosphere is driven by the influx of root exudates and rhizodeposits (sloughed-off dead root tissues) rich in various organic compounds.

The diverse microbial population of the rhizosphere does not constitute an obligate root microflora, yet it exerts a profound influence on vital plant physiological processes, including Respiration, Photosynthesis, Fertilization, and phosphate and Nitrogen METABOLISM. For instance, rhizosphere bacteria produce thiamine and other Vitamins, break down complex organic compounds making them accessible to plants, and synthesize growth stimulants such as Gibberellins and heteroauxin. The presence of a diverse bacterial community within the rhizosphere fosters competition for nutritional substrates, thereby suppressing the proliferation of opportunistic forms, including phytopathogens. Heterotrophic gracilicutes rods predominate in the rhizosphere. While the rhizosphere microbial composition varies among plant species, strict specificity of particular bacteria to specific plants is not observed. For example, alongside ubiquitous forms, characteristic species are found in the rhizosphere of various crops: Rhizobium meliloti, Pseudomonas ocawthe, P. liquida, and P. carnea in alfalfa; P. sinuosa, P. caudatus, and Aerobacterium liquefaciens in maize.

The most intensive bacterial proliferation in the rhizosphere occurs during periods of active Plant Growth and pre-flowering. Following the completion of annual plant development or the dieback of perennial roots, the roots begin to serve as a nutrient source. During this phase, the rhizosphere composition shifts: bacteria utilizing pectin and cellulose proliferate, and the proportion of Gram-positive forms increases.

The roots of most higher plants maintain a close symbiotic association with fungi. This form of symbiosis, like many others, establishes dynamic conditions of mutual exploitation from which both partners derive benefit. As a result of this interaction, the root Structure is modified in a specific manner. This complex structural unit, comprising higher plant roots and fungal hyphae, is termed a mycorrhiza.

The presence or absence of mycorrhizae, as well as their structural features, are primarily determined by the taxonomic position of the host plant. Among HIGHER SPORE PLANTS, the sporophytes of clubmosses and horsetails lack mycorrhizae. All gymnosperms are mycotrophic. Among angiosperms, mycorrhizae occur less frequently in Cyperaceae, Juncaceae, Brassicaceae, Papaveraceae, Caryophyllaceae, Polygonaceae, and Chenopodiaceae than in other families. Leguminous plants, which form symbioses with root-nodule bacteria, also possess mycorrhizae. It is estimated that nearly 90% of vascular higher plants feature mycorrhizal roots. Mycorrhizal roots are thicker and exhibit increased branching. Mycorrhization induces both morphological and cytological alterations in the root (Fig. 8.6).

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Fig. 8.6. Mycorrhization of roots:

a — morphological changes: 1 — Prunus cerasifera colonized by the fungus Glomus sp.;

2 — non-mycorrhizal roots; b — cytological changes: 3 — cross-section of the root apex of non-mycorrhizal Allium porum;

4 — colonized by the fungus Glomus sp.

According to V. Williams, "mycotrophism is a mechanism by which higher green plants assimilate ash elements and nitrogen from an environment containing these nutrients in the form of organic matter preserved under anaerobic conditions. In this process, nutrition is mediated through the symbiotic coexistence of green plants and fungal mycelium. The mycotrophic type of plant nutrition is arguably more widespread in nature than autotrophy."

The Morphology and structure of mycorrhizae can vary considerably. Ectomycorrhizae, endomycorrhizae, and transitional (ectomyndomycorrhizae) forms are distinguished.

Ectomycorrhiza (Fig. 8.7) is characteristic of the vast majority of forest trees. In this type, the root is densely enveloped by a fungal mantle (sheath), from which a dense network of hyphae extends. The fungal hyphae penetrate the root to a shallow depth without affecting the central cylinder (primarily reaching the intercellular spaces of the exodermis, where they intertwine to form the so-called Hartig net). The fungal mantle encloses the root so tightly that root hairs disappear, while water and nutrients are absorbed directly by the fungal mycelium. Only the main root tips remain immune to the fungus. Mycorrhizae of this type can

be formed by various fungi, whose individual characteristics determine the color and appearance of the mantle. The fungal mantle is most commonly whitish, pink, or even black. Ectomycorrhiza is an annual structure that regenerates every year.

Species that form ectomycorrhizae exhibit varying degrees of host specificity. Typical mycorrhizal species establish a mutualistic feeding strategy (capable of supplying the plant with essential phosphorus and nitrogen sources while receiving carbon sources in return). Non-specific ectomycorrhizal fungi can form a symbiosis with higher plants, and in the absence of the latter, they live as typical heterotrophs. According to paleomycology data, ectomycorrhizal fungi are among the most ancient. Roots with ectomycorrhiza date back approximately 50 million years.

Fig. 8.7. Ectomycorrhiza:

a - cross-section of a rowan rootlet enveloped by a fungal mycelium sheath; b - root cluster of a mature oak, representing a coral-like mycorrhiza

Endomycorrhizal type (Fig. 8.8) is found in orchids, ericaceous plants, perennial grasses, and on the root systems of many trees and shrubs. It differs from ectomycorrhiza in that the fungal mycelium spreads not only between the Cells of the cortical parenchyma but also penetrates directly into them. At the same time, the cortical parenchyma cells remain viable and can even digest the invading mycelium. Under The Influence of plant cell contents, the intracellular fungal mycelium may form coils (pelotons), sometimes tree-like branchings (arbuscules), or swellings at the hyphal tips (sporangioles and vesicles). The central cylinder of the plant root always remains

free from infection. Some of the mycelial terminals emerge into the soil without forming a fungal mantle. Unlike ectomycorrhiza, the plant's root hairs are always preserved in endomycorrhiza and can fully perform their physiological functions.

Fig. 8.8. Endomycorrhiza of wheat

Endomycorrhizae are formed with the participation of species from the genus Glomus (phylum Zygomycota). They supply the plant with readily available phosphorus compounds while assimilating the plant's carbon compounds. Furthermore, the presence of ecto- and endomycorrhizal species enhances plant viability and resistance due to the increased adsorption capacity of the fungal mycelium toward toxins, heavy metals, and radionuclides. The latter remain trapped in the mycelium and do not enter the plant. The presence of symbiotic fungi protects the plant from root phytopathogens, notably species of the genera Fusarium, Phoma, Rhizoctonia, and others.

Transition-type mycorrhiza possesses the characteristics of both previous types.

Peritrophic mycorrhiza is occasionally observed, in which the mycorrhiza-forming fungus does not establish a close intimate connection with the plant. They colonize the rhizosphere, enveloping the root. In some cases, pseudomycorrhizae are formed by parasitic fungi.

Based on their interactions with mycorrhiza-forming fungi, higher plants are divided into the following groups:

- obligately mycotrophic plants, which cannot develop without a fungus (ghost pipe, orchid);

- plants that improve their GROWTH AND DEVELOPMENT in the presence of mycorrhiza. This group includes trees (hornbeam, oak, conifers, etc.), shrubs, and herbaceous plants;

- plants that develop without mycorrhizae. These are typically aquatic plants and a small group of terrestrial plants.

Mycorrhiza in the same plant can be formed by different fungi capable of entering into symbiosis with it. The same fungus can form mycorrhiza with different plants, although certain fungi exhibit a specific host preference. This explains the rather characteristic composition of mushroom flora (agarics) under various forest tree species.

True mycorrhizae significantly enhance the development of both The Root System and the above-ground PARTS OF THE plant.

Another type of endosymbiotic relationship occurs between rhizobia (nodule bacteria) and leguminous plants (nodule formation). There are two known pathways for nodule bacteria to penetrate the plant root: through root hairs and via "splits" formed at the base of lateral root branches. Plants infected through lateral hairs show higher specificity toward the symbiotic partner.

Within the root Hair, the bacteria form a so-called infection thread—a mucilaginous mass filled with intensively multiplying bacterial cells. From the root hair, this thread penetrates through the cortical cells into the parenchyma. As it grows, the infection thread becomes covered with a cellulose wall synthesized by the plant.

Nodule bacteria are able to proliferate only within the plant's tetraploid cells. When the infection thread penetrates these tetraploid cells, some of the bacteria pass from the thread into the Cytoplasm of the PLANT CELLS AND begin to multiply there. These cells, in turn, stimulate the division of neighboring cells, thus forming the nodule tissue. The bacteria that have entered The plant cell cytoplasm grow and divide, but eventually transform into bacteroids—cells incapable of further division. In plant cells, bacteroids are most commonly located within vacuoles. Bacteroids contain more poly-β-hydroxybutyric acid, Glycogen, and polyphosphates than free-living cells, but less DNA. Bacteroids become functionally similar to nitrogen-fixing Organelles of the host plant.

Actively nitrogen-fixing nodules are typically red due to the presence of leghemoglobin, which can be detected as early as the second day after nodule formation. Nitrogen fixation begins on the fourth day. Both symbionts—the plant and the bacteria—participate in the synthesis of leghemoglobin, a crucial product of symbiosis. When bacteria and plants are cultured separately, leghemoglobin is not produced by either. Leghemoglobin has two distinct properties: it can undergo oxidation and reversibly bind oxygen. Leghemoglobin is located within the vacuoles of the PLANT CELL AND is easily washed out with water. It is believed to facilitate nitrogen assimilation by maintaining the redox state at a specific level.

Symbiotic systems such as rhizobia-legumes serve as an example of a complex yet highly organized symbiosis (involving direct Gene exchange) between organisms belonging to different kingdoms.

In addition to positive interactions, negative relationships can also arise between bacteria and plants. Bacteria that parasitize plants are called phytopathogens. Phytopathogenic bacterial species are found among aerobic and facultatively anaerobic Gram-negative rods (Pseudomonas, Xanthomonas, Erwinia, Agrobacterium, etc.), as well as among Gram-positive coryneform bacteria and Mycoplasmas. Like animal pathogens, plant pathogens possess pathogenicity factors that allow them to overcome plant defense barriers. These factors include the enzymes pectinase and cellulase, as well as phytotoxins and adhesion factors.

Bacteria infect plants by penetrating through Stomata or lenticels, and can occasionally be transmitted through seeds. Some bacteria are capable of entering the plant exclusively through fresh mechanical injuries (minor wounds). For instance, the causal agent of bacterial canker in tomatoes infects the plant when trichomes on the stem or fruit are broken. Insect vectors frequently facilitate plant infection. Erwinia amylovora is carried by bees and enters the plant through nectaries. Erwinia stewarti, a corn pathogen, is disseminated by beetles and infects the plant through feeding wounds. Bacterial cells reside in the saliva and gut of insects and are even able to overwinter there.

Once inside the plant, phytopathogenic bacteria typically proliferate in the intercellular spaces and Vascular System. They induce various rots, blights, spots, and tumor-like growths.

Specific relationships have evolved between phytopathogenic bacteria and plants, involving processes of mutual recognition followed by physiological and regulatory responses. Bacterial recognition of the plant can stimulate its defense mechanisms, with plant Lectins playing a significant role in this process.

An important factor in Plant resistance to phytopathogenic bacteria is the production of phytoalexins—low-molecular-weight compounds possessing bactericidal properties. Phytoalexins are absent in healthy plants. The synthesis of phytoalexins can be induced by various compounds, including Components of the Introduction/37.html">Bacterial cell wall.

Interactions between microorganisms and invertebrates. Microbial endosymbionts are widespread among Protozoa, worms, insects, and other invertebrates.

Bacterial cells have repeatedly been detected in the cytoplasm, vacuoles, and nuclei of amoeboid cells. The functions of such symbiosis remain insufficiently studied. It is hypothesized that in amoeba cells lacking Mitochondria, bacteria perform these exact mitochondrial functions.

Research into anaerobic microorganisms led to the discovery of their symbiotic relationships with marine amoebae and Ciliates. Methanogenic archaebacteria have been found within the cells of these animals, associated with microbody-like organelles known as hydrogenosomes, where Pyruvate is converted into hydrogen, CO₂, and acetate. Methanogens utilize these metabolic byproducts to produce methane. For the host, these symbionts act as TERMINAL ELECTRON ACCEPTORS, while the archaebacteria find protection and a nutrient source within the protozoan cell.

A fascinating example is the tripartite symbiosis involving bacteria, protozoa, and insects. Wood-feeding cockroaches and termites, for instance, harbor a large population of flagellated protozoa within their guts. These flagellates densely pack the sac-like expansion of the insect's hindgut. In turn, the flagellates themselves host extracellular spirochetes and intracellular bacteria. This close coexistence of microorganisms and protozoa results in the production of the enzyme cellulase, which enables the insects to digest wood. One of the most remarkable Features of the symbiont transmission cycle in these insects is that encystment in flagellates is regulated by Insect Hormones.

Antibiotics can be used to rid insects of their symbionts. Symbiont-free cockroaches are poorly pigmented, less active, develop slowly, do not avoid light unlike normal individuals, and ultimately degenerate. It is suggested that the symbiont supplies the host with certain nitrogen-metabolism enzymes that are particularly essential for the insect during its larval stage.

Symbiosis with bacteria is also a characteristic feature of cicadas. Over 50 types of symbionts have been described in them, and individual cicadas may harbor anywhere from one to six symbionts simultaneously. In addition to bacteria, cicadas frequently feature

fungi as symbionts. These symbionts are passed on to offspring via the eggs. Symbiont cells have an irregular shape and appear somewhat unusual on ultrathin sections. They are surrounded by three membranes: two of their own, and a third formed by the host. DNA-containing zones are not detectable. Notably, viable cicada offspring develop exclusively from eggs infected with symbionts.

Another compelling example of symbiotic interaction is the association between pogonophorans and bacteria. One species of such symbionts inhabits depths of 2500 m near the Galapagos Islands. A unique feature of this life form is its complete independence from solar energy, as it relies entirely on geothermal energy. Pogonophorans completely lack a digestive tract, and metabolism occurs directly through the epidermis. Nutrition is sustained by processes taking place within trophosomes—specialized animal tissue structures containing bacteriocyte cells. Bacteriocytes are densely packed with gram-negative bacterial cells. The water inhabited by pogonophorans contains significant concentrations of hydrogen sulfide, which is oxidized by the bacterial symbionts. Trophosomes feature a highly branched vascular system. Oxygen (O₂) and carbon dioxide (CO₂) are delivered to the bacteria via the Blood. Cells harboring symbionts contain cytoplasmic Hemoglobin, which facilitates Oxygen transport to the symbionts across the cytoplasm. Autotrophic bacteria synthesize organic compounds using energy derived from The oxidation of hydrogen sulfide. The products of Chemosynthesis serve as the sole source of nutrition for both the microorganisms and their host.

Virtually any bacteria can fall prey to invertebrates—ranging from amoebae to Mollusks and mites—which consume them as food. The Fate of bacterial cells ingested by an invertebrate can vary. If the animal possesses appropriate hydrolytic enzymes capable of degrading bacterial cell walls, the bacteria are digested. If such enzymes are lacking, the microorganisms remain viable and occasionally proliferate intensively within the invertebrate's body.

Interactions between MICROORGANISMS AND THE human body. As a result of mutual adaptation between micro- and macroorganisms forged through evolution, the so-called normal microflora of The Human Body has formed. Certain microorganisms enter the human body via water, air, and food, residing there only transiently. A substantial proportion of bacteria has adapted to colonize specific body sites; consequently, discussions of normal microflora distinguish between the microflora of the Skin, oral cavity, gastrointestinal tract, respiratory and urinary tracts, as well as the conjunctiva and Vagina.

Skin microorganisms. Human skin surfaces vary in topography and regional characteristics. Epidermal cells are constantly sloughed off and renewed. Sweat and sebaceous gland secretions are released onto the skin surface, providing a nutrient-rich medium for microorganisms. Sweat Glands supply bacteria with salts and organic compounds, including nitrogenous substances, while sebaceous secretions are rich in Lipids.

Sweat glands are abundant (~300/cm²) on the soles, palms, and armpits, and fewer (up to 100/cm²) on the back. Microorganisms predominantly colonize areas of skin covered with hair and moistened with sweat. For instance, the axillary region harbors 10⁵-10⁶ bacterial cells per cm². Hair-covered skin areas contain ~1.5 · 10⁶ cells/cm², whereas only a few hundred bacteria inhabit 1 cm² of the back.

The cutaneous microbiota is typically dominated by gram-positive bacteria: Staphylococcus (S. epidermidis, S. hominis), Micrococcus, Propionibacterium, Corynebacterium, Brevibacterium, and Acinetobacter.

Representatives of the genus Corynebacterium sometimes account for up to 70% of the total skin microflora. Certain species produce lipases that break down lipids (sebaceous secretions). Sterile sweat is odorless; its characteristic odor is generated by bacterial metabolic products, primarily those of Corynebacterium.

The skin of the feet is characterized by an Abundance of Brevibacterium cells, which metabolize Sulfur-Containing Amino Acids to produce methanethiol gas, yielding a distinct odor.

Human skin is continuously contaminated by soil and airborne microorganisms, which may include opportunistic and pathogenic agents (staphylococci, as well as the causative agents of tetanus, gas gangrene, and botulism). However, in healthy individuals, the normal skin microflora and other defense mechanisms prevent the onset of infectious processes.

The conjunctiva harbors a sparse microbial population, owing to the presence of Lysozyme in tear secretions. Conjunctival microorganisms include staphylococci and corynebacteria. In some cases, mycoplasmas, Adenoviruses, and Herpesviruses are detected, which can trigger infections when host defenses are compromised. In a significant percentage of people (~47%), conjunctival microflora is completely absent.

Ear microflora. The inner and Middle ear should normally be sterile. The external auditory meatus frequently harbors facultative microflora comprising non-pathogenic staphylococci and corynebacteria; less commonly, bacteria of the genus Pseudomonas, Yeast-like fungi of the genus Candida, and Molds (such as Aspergillus) may be present, which under certain conditions can cause pathological processes.

Urogenital microflora. The Kidneys, Ureters, and urine within the Urinary Bladder are normally sterile. The external genitalia harbor mycobacteria (Mycobacterium smegmatis), corynebacteria, mycoplasmas, and staphylococci. Vaginal microflora undergoes regular succession across different stages of life. In girls, the initial microorganisms appear within 24 hours after birth. The first month of life is dominated by lactobacilli (Lactobacillus acidophilus, L. fermentum) transmitted from the mother during delivery. Optimal conditions exist for the proliferation of lactic acid bacteria during this period, as the infant's body is saturated with estrogenic hormones, and the vaginal secretion contains glycogen and exhibits an acidic reaction. Concurrently, staphylococci (S. saprophyticus), streptococci (S. faecalis), corynebacteria (C. xerosis), and other taxa are detected in the vagina.

Over the subsequent decade, microorganisms are virtually undetectable in the vagina. During this phase, maternal hormones acquired at birth disappear, the pH of the vaginal secretion shifts to neutral or slightly alkaline values, and glycogen vanishes. With the onset of Puberty, lactic acid bacteria reappear, driven by the endogenous estrogenization of the body and the lowering of the vaginal pH to an acidic range. During menstrual cycles, the secretion becomes alkaline, leading to the detection of staphylococci, non-hemolytic streptococci, mycoplasmas, yeast-like fungi, and protozoa alongside lactic acid bacteria and corynebacteria.

Microorganisms of the respiratory tract. Over the course of a day, an adult inhales approximately 12,000–14,000 liters of air, which introduces dust particles and adsorbed microorganisms into the body. Exhaled air contains 250 to 500 times fewer microbial cells than inhaled air. The bulk of microorganisms is trapped on the mucous membranes of the Upper Respiratory Tract, where they are subjected to the bactericidal action of lysozyme and mucin, or expelled back into the environment through sneezing.

Several permanent species of non-pathogenic staphylococci (Staphylococcus epidermidis, S. saprophyticus), certain corynebacteria, streptococci, and diphtheroids are typically found in the Nasal cavity. Facultative microflora is represented by Staphylococcus aureus, Streptococcus pyogenes, S. pneumoniae, neisseriae (Moraxella lacunata), haemophilic bacteria (Haemophilus influenzae), and others.

The mucous membranes of the nasopharynx harbor Streptococcus mitis, along with certain non-pathogenic neisseriae and veillonellae. The facultative nasopharyngeal microflora includes Neisseria meningitidis, Streptococcus pneumoniae, and mycobacteria.

Microorganisms residing in the nasopharynx are potentially capable of migrating into the Lungs. However, a wide range of defense mechanisms prevents them from penetrating the Trachea, Bronchi, and lungs. First, the majority of bacteria adhere to the nasopharyngeal mucosa and cannot move freely toward the lungs, as the ciliated epithelial cells lining the trachea continuously propel mucus upward. Second, the lungs serve as a site of very active phagocytosis—a mechanism whereby foreign cells are engulfed and inactivated.

Microorganisms of the digestive tract. The oral cavity hosts nearly 100 species of commensal microorganisms, with 1 mL of saliva containing upwards of 10⁸ microbial cells. This environment offers ideal conditions for the proliferation of both saprophytic, pathogenic, and opportunistic species. Saliva plays a paramount role in maintaining the quantitative and qualitative diversity of oral microflora. It supplies essential nutrients while maintaining a constant temperature, pH, moisture level, and other conditions favorable for Microbial growth. At the same time, saliva exhibits distinct antibacterial properties due to enzymes such as ptyalin, lysozyme, lactoferrin, peroxidase, and nuclease, and it contains specific secretory IMMUNOGLOBULINS.

The quantitative and qualitative composition of a child's oral microflora depends on their age and diet. Within a few days after birth, streptococci (Streptococcus salivarius, S. mitis), lactobacilli, certain neisseria species, and actinomycetes can be detected in the oral cavity. As a person ages, this microbial composition undergoes Qualitative and quantitative shifts.

The bulk of the oral microflora is localized in dental plaque and on the dorsum of the Tongue. Microorganisms account for nearly 70% of dental plaque volume, with approximately 2.5 x 10⁸ microbial cells identified in every 1 mg of its dry mass.

The most typical microorganisms found in the adult oral cavity include streptococci (Streptococcus salivarius, S. mitis, S. mutans, S. sanguis, and occasionally S. faecalis), hemolytic streptococci, lactobacilli, veillonellae, saprophytic neisseriae, bacteroides, and corynebacteria.

Other microorganisms detected in the oral cavity include haemophilic bacteria (Haemophilus influenzae), treponemes (Treponema denticola, T. macrodentium, T. oralis), yeast-like fungi (Candida albicans), actinomycetes, mycoplasmas (Mycoplasma oralis, M. salivarium), and others.

Among the facultative residents of the oral cavity are enterobacteria (representing the genera Escherichia, Enterobacter, Klebsiella, Proteus), Pseudomonas aeruginosa, as well as endospore-forming bacteria of the genera Bacillus and Clostridium.

Dental and gum diseases can be triggered by shifts in the quantitative and qualitative makeup of the normal microflora, as well as by poor oral hygiene. Streptococcus mitis, a member of the normal flora, can cause inflammation of the dental pulp when it colonizes the crevices between the Gums and the tooth surface. S. salivarius is found predominantly in saliva and on the dorsum of the tongue; it produces significant amounts of dextran- and levan-type mucilaginous substances and can contribute to dental caries. S. sanguis localizes in dental plaque, produces a dextran-type mucilaginous substance, and is likewise recognized as a potential cause of dental caries.

Upon entering The Stomach, the majority of transient microorganisms perish. This is facilitated by low pH levels and high activity of hydrolytic enzymes, which exert a bactericidal effect and form a reliable barrier against the penetration of microorganisms into the intestine. Nevertheless, gastric juice acidity is not constant; it fluctuates depending on The Nature of the food and fluid intake. Small quantities of lactic acid bacteria, sarcinae (Sarcina ventriculi), bacterial spores, and Yeasts (up to 10³ per 1 mL) can be detected in the stomach. In certain cases, dysentery, typhoid, paratyphoid bacilli, cholera vibrios, and other pathogenic or opportunistic microorganisms may find their way into the stomach and subsequently into the intestines.

The Small Intestine, particularly its upper sections, contains a relatively small number of microorganisms—predominantly aerobes—not exceeding 10²-10³ cells, despite the alkaline reaction of the environment. Rapid microbial proliferation is suppressed by the bactericidal enzymes secreted in the small intestine. In the lower section of the small intestine, the microflora is more abundant and closely resembles that of the Large Intestine in its composition.

The large intestine provides the most favorable environment for the development of numerous microbial species. The composition of intestinal microflora shifts throughout a person's life. The intestine of a newborn is sterile During the first hours of life. Over time, a specific microflora develops, consisting of 85–95% bifidobacteria and lactobacilli. These bacteria exhibit antagonistic properties against pathogenic and opportunistic microorganisms capable of causing intestinal disorders in infants. By the 3rd to 5th day, E. coli and enterococci appear in the infant intestine, and their population increases as the child transitions to a mixed diet. Bacteroides are typically undetectable in children during the first six months of life.

The large intestine of an adult harbors over 400 species of diverse facultative and obligate anaerobes (~10⁹ microbial cells per 1 g of content). The dominant group characteristic of adult eubiosis consists of asporogenous anaerobic bacteria—bifidobacteria and bacteroides. Among facultative anaerobes, Escherichia coli, lactobacilli, and enterococci predominate. Representatives of the genus Clostridium (C. perfringens, C. sporogenes), Proteus, Staphylococcus, Pseudomonas, and yeast-like fungi (Candida albicans) are found in minor quantities (up to 10³ per 1 g of content).

Normal Human and Animal microbiocenoses are generally viewed as a unique microecological system that performs and regulates a series of vital host functions. One of the primary Functions of the normal microflora is to prevent the colonization of the macroorganism by pathogenic bacteria. This is achieved both through the high adhesive Properties of the normal microbiota (i.e., its superior competitiveness in colonizing Epithelial Tissues) and through the production of substances that inhibit pathogen growth while establishing an unfavorable pH level. The involvement of the normal flora in shaping the protective and adaptive mechanisms of the macroorganism has also been proven. For instance, normal microflora microorganisms participate in regulating immunoglobulin synthesis, stimulate The activity of phagocytic cells localized in the intestinal wall along with their bactericidal activity, and take part in the metabolic transformation of certain substances (e.g., primary Bile acids are transformed into secondary ones under the influence of bacteroides). The inactivation of certain enzymes and toxins also occurs with the participation of normal flora members. Furthermore, it is well established that the normal flora contributes to the metabolic processes of the macroorganism; specifically, bifidobacteria synthesize amino acids, Proteins, vitamins B₁, B₂, K, thiamine, riboflavin, nicotinic, pantothenic, and folic acids, pyridoxine, and cyanocobalamin, while also facilitating the absorption of calcium, iron, and vitamin D.

Thus, the normal microflora maintains a direct and intimate connection with the macroorganism. At the same time, it serves as a highly sensitive indicator system that responds with quantitative and qualitative disturbances to any alterations within the macroorganism.

The evolutionarily shaped macroorganism–normal microflora system is constantly subjected to various environmental factors, including diet, seasonality, occupation, surgical interventions, X-ray, radiation, and Chemotherapy, among others. All of these factors (individually or in combination) can negatively impact the dynamic equilibrium between the macroorganism and its microbiocenosis. Disturbances in the microbiocenosis involving the total count of microorganisms and/or The ratio of individual species and their properties are referred to as dysbiosis. Intestinal dysbiosis is the most common form.

Factors leading to alterations in the composition of the normal microflora include a person's age, dietary habits, shifts in ecological and climatic conditions, and emotional state (stress). This is classified as primary dysbiosis. Conversely, alterations in microflora composition resulting from specific diseases or their Treatment are referred to as secondary dysbiosis.

With advancing age, virtually all elderly individuals experience age-related dysbiosis, which is accompanied by impaired intestinal motility and enhanced absorption of microbial metabolic products, ultimately affecting Cholesterol and Bile acid metabolism. Metabolic byproducts that should be excreted through the intestines are retained, leading to an increase in microbial populations within non-sterile areas of the body, along with alterations in their COMPOSITION AND PROPERTIES (such as The Emergence of enzymatically defective strains of E. coli, alongside its hemolytic and capsular forms).

Dietary dysbiosis occurs when There is a shift in dietary regimen and patterns. A diet predominated by dairy products leads to an increase in acidophilic bacteria, Citrobacter, and fungi, while decreasing the counts of Escherichia coli and spore-forming microorganisms. A meat-rich diet, by contrast, increases the populations of E. coli and spore-forming aerobes while reducing acidophilic microflora. The underlying cause of these compositional and functional shifts under different dietary regimes is the alteration of biochemical processes within the large intestine.

Seasonal dysbiosis is associated with temperature fluctuations and dietary changes. The biological properties of microorganisms can vary depending on ambient temperature. As external temperatures rise, microbial populations may undergo a phase transition from a latent to an active state, accompanied by an intensification of the epidemic process. Specifically, an increase in intestinal infections correlates with rising temperatures, which activate both the disease-causing agents themselves and their transmission routes. In most cases, winter dysbiosis is accompanied by constipation, whereas summer dysbiosis typically manifests as diarrhea.

Primary dysbiosis also encompasses dysbiotic shifts that occur in clinically healthy individuals under the influence of stressful situations.

During a stress response, the intestinal microbial reaction is accompanied by species-level restructuring, a breakdown of the ecological barrier, and the creation of conditions conducive to colonization by opportunistic pathogens. Stress-induced changes exert their most profound impact on the Digestive System and human immunological status. For example, alterations in the digestive tract are marked by weakened intestinal peristalsis and a compromised barrier function resulting from morphofunctional Changes in the mucosa. Furthermore, stressful situations induce modifications in both the adhesive properties of bacteria and the adhesiveness of the macroorganism. The superficial mucous layer of the intestinal mucosa, composed of mucin, plays a crucial role in the multifactorial process of bacterial adhesion to its surface. The physicochemical state of mucin can be readily disrupted by bile acids, Proteolytic Enzymes, and pH fluctuations. During a stress reaction, there is a sharp depletion of mucin and a reduction in acidic mucopolysaccharides on the surface of the intestinal mucosa and within its surface-covering cells. Another factor contributing to altered adhesion during stress is the disruption of hormonal Homeostasis, as hormones induce changes in the synthesis of bacterial receptors and modify the capacity of respective host cells to bind bacterial cells. Stressful states also alter immunoreactivity, characterized by a decrease in IgA levels, whose role in defending against pathogenic agents is closely linked to the suppression of adhesion and colonization.

A decline in the immunological resistance of the macroorganism can significantly affect the topographical distribution of individual microbial groups within the gastrointestinal tract—a factor of critical importance regarding endogenous contamination and the metabolic consequences of overgrowth in the small intestine. It should be noted that virtually all Types of Metabolism are disrupted during human stress responses.

In most cases, primary dysbiosis encompasses alterations in intestinal microflora composition that are unaccompanied by pronounced clinical symptoms, require no specialized treatment, and generally resolve spontaneously once the triggering factor is removed.

An expressly isolated form of dysbiosis should be considered to include changes in the composition of the normal microflora that occur under the influence of ionizing radiation.

Since the second half of the 20th century, due to the development of the nuclear industry and power engineering, as well as medical and domestic radiation equipment, the release of radioactive substances into the environment has been continuously increasing. Nuclear weapons testing, accidents at nuclear facilities, and the improper handling of radiation equipment all lead to the emergence of large and small regions with elevated radiation levels. The impact of ionizing radiation on the human body does not go unnoticed, and the probability of pathological changes increases with higher radiation doses.

The response of the digestive tract to irradiation is a set of complex changes that affect the intestinal mucosa, disrupt Blood Circulation in the vessels, and alter secretion, motility, and absorption processes. In mucosal cells, Protein Synthesis AND enzymatic activity are sharply suppressed, massive death of epithelial cells is observed, and their division decreases. At low doses of irradiation, the number of Escherichia coli, staphylococci, Proteus species, and clostridia increases in the intestine, while the content of lactobacilli declines. The numbers of yeasts and bacteroides remain unchanged.

Following irradiation, the permeability of the intestinal walls increases significantly, facilitating The entry of toxic products—produced by harmful microorganisms—from the digestive tract into the blood. In microbial intoxication during radiation sickness, a certain role is played by the toxins of clostridia, staphylococci, streptococci, and other bacteria, that is, the toxins of all microorganisms present on the mucous membrane. Importantly, these bacteria are capable of establishing an associative relationship with the intestinal mucosa, and the diarrhea that occurs during acute radiation sickness is likely associated with the penetration of enterotoxin-producing strains into the mucosa. It is believed that a decrease in the number of colicinogenic Escherichia coli in the intestine correlates with an increase in the number of pathogenic and antibiotic-resistant strains.

Under the action of high radiation doses, animals die on days 3–4, and post-radiation dysbiosis does not have time to develop. It develops gradually, 6–8 days after irradiation.

Under the influence of ionizing radiation, the resistance of the macroorganism to infection by various infectious agents is significantly reduced. The course of infectious diseases is characterized by generalization of the process, accumulation of substantial amounts of microorganisms, transition of chronic diseases with a latent course into manifest acute forms of the illness, development of destructive-necrotic inflammatory processes in tissues, shortened life expectancy, and increased mortality.

Regarding the impact of ionizing radiation on the microflora of the human body, several general Conclusions can be drawn, specifically:

- irradiation causes the death of microorganisms, with the Number of viable cells decreasing as the radiation dose increases; this demonstrates its lethal effect;

- irradiation exhibits a mutagenic effect, leading to the appearance of hereditarily altered forms. To a certain extent, the number of mutants increases with higher doses;

- Variability caused by irradiation is non-directed and stochastic in nature (among the surviving forms, microorganisms with various changes in morphological, physiological, and biochemical properties can be found);

- among mutant microorganisms, forms with negative (less viable) and positive (more viable) changes can be distinguished.

Secondary forms of dysbiosis include dysbiotic changes that accompany the underlying disease or result from its therapy. The fact that these changes are secondary is evidenced by the observation that in the first days of the illness, the intestinal microflora is qualitatively diverse with a fixed ratio of normal flora representatives against the Background of an increase in certain species of opportunistic and pathogenic microorganisms. Only over time does the specific weight of bifidobacteria and lactobacilli decrease, and the balance between anaerobic and aerobic microflora is disrupted. Since colonizing resistance of the intestine is provided by anaerobic microorganisms, a decrease in their number facilitates the penetration of pathogenic microorganisms through the intestinal mucosa. Furthermore, in various pathological conditions of the digestive Organs, microorganisms colonize the upper sections of the small intestine, which is an important sign of dysbiosis.

Functional and morphological changes in the intestinal walls (for example, in enterocolitis) facilitate the penetration of microorganisms. In addition, during inflammatory processes in the small intestine and the presence of microorganisms therein, The rate of epithelial regeneration is inhibited, mucosal atrophy develops, which is accompanied by a decrease in the adsorptive capacity of epithelial cells. Due to impaired membrane Digestion, incompletely hydrolyzed products accumulate in the intestinal lumen, absorption is disrupted, and osmotic pressure increases, leading to the onset of enteric syndrome (diarrhea, intestinal rumbling, bloating). Simultaneously, large bowel dysfunction occurs. Microbial metabolites and toxins exert local and general effects on the human body. Microorganisms lose their ability to inactivate digestive enzymes entering from the upper parts of the digestive tract, which is why fecal intestinal enzymes (enterokinase and alkaline phosphatase) are excreted in large amounts during dysbiosis.

An equally important consequence of dysbiosis is the disruption of the intensity of endogenous synthesis and assimilation of vitamins. The assimilation of iron, calcium, and biologically active compounds, as well as the absorption of carbohydrates, Fatty acids, amino acids, and nitrogen compounds, is also impaired.

Sensitization and allergization of the macroorganism in dysbiosis lead to a prolonged course of the underlying disease, an increase in histamine levels, and the inability of the damaged intestinal mucosa to produce sufficient quantities of histaminase to inactivate the histaminogenic microflora.

The treatment of these changes with antibiotics, in turn, leads to disruptions in the composition of the normal microbiocenosis.

The dynamics of changes in intestinal microflora depends on the dose of the antimicrobial drug. When small and medium therapeutic doses of antibiotics are used, the number of opportunistic microorganisms increases directly during antibiotic therapy. The Use of broad-spectrum antibiotics in high therapeutic doses is accompanied by a disruption of biofilm integrity, up to its complete disappearance from a significant portion of the intestinal surface. Persistent and pronounced dysbiosis develops immediately after the cessation of antibiotics. The vacated spaces on the intestinal mucosa are occupied by environmental microorganisms. These microorganisms differ from the representatives of the normal flora in that they are unable to perform A number of important physiological functions, thereby disrupting metabolic processes in the intestine.

The use of antibiotics leads to an increase in resistant microorganisms. The elevated level of antibiotic-resistant bacteria is driven by both selective proliferation and the transfer of the R-factor (resistance factor) to related bacteria.

It should be noted that global changes in the composition of the intestinal normal flora occur not only in gastrointestinal infections (salmonellosis, staphylococcal gastroenterocolitis, campylobacteriosis, etc.), but also in infectious diseases not localized in the gastrointestinal tract, such as acute respiratory diseases. In these cases, a decrease in bifidoflora, an increase in the number of E. coli with altered enzymatic properties, and the appearance of its hemolytic forms are observed. At later Stages of the disease, Staphylococcus aureus, Pseudomonas aeruginosa, and P. alcaligenes predominate in the intestinal microbiocenosis. It must be emphasized that the microflora of the digestive tract in humans recovers much later than Clinical Recovery occurs.

All changes arising under the influence of various factors on the macroorganism can be more or less pronounced; therefore, in clinical practice, it is customary to determine the degree of severity of dysbiosis.

The most successful scheme for determining the degree of dysbiosis is considered to be the one proposed in 1986 by N. Grachyova. According to this scheme, four degrees of dysbiosis are distinguished:

- 1st degree dysbiosis (latent, compensated form) is characterized by minor changes in the aerobic part of the microbiocenosis (an increase or decrease in the number of Escherichia coli). Bifido- and lactoflora remain unchanged. Intestinal dysfunctions are generally not recorded;

- 2nd degree dysbiosis (subcompensated form). Against the background of a slight decrease in the content of bifidoflora, quantitative and qualitative

changes in Escherichia coli or other opportunistic microorganisms are detected. This form of dysbiosis is a borderline state and indicates that the subjects examined can be classified as a risk group;

- 3rd degree dysbiosis is characterized by a significant decrease in the level of bifidobacteria along with lactobacilli and drastic changes in the number of Escherichia coli. Conditions are created for the manifestation of pathogenic properties in opportunistic microorganisms. Intestinal dysfunctions occur;

- Grade 4 dysbiosis is characterized by the complete absence of bifidobacteria, a significant decrease in lactobacilli, and profound alterations in Escherichia coli. The quantity of opportunistic microbiota—both facultative and uncharacteristic of a healthy individual—increases markedly.

Timely detection of dysbiosis and accurate assessment of its severity enable the prompt and appropriate Selection of Methods and Means to restore the human normal microbiocenosis.