Mycoplasmas l do not have a form. cultural properties
Mycoplasmas are characterized by extremely pronounced polymorphism, primarily due to the absence of a solid cell wall inherent in bacteria, as well as a complex development cycle. The smallest structural elements capable of reproduction in artificial nutrient media are commonly called minimal reproductive units. The shape and size of the minimum reproductive units, as well as cellular elements of different stages of development, are significantly affected by the cultivation conditions, the physicochemical properties of nutrient media, the characteristics of the strain and the number of passages on the media, the technique of preparing, fixing and staining preparations, and other factors.
Due to the fact that mycoplasmas do not have a cell wall, their membrane and cytoplasm are easily damaged by chemical reagents used for fixing and staining preparations. Mycoplasma cells in the early stages of development are especially sensitive to environmental factors.
In smears from the affected organs and from cultures grown in the environment, mycoplasmas are represented by round, oval and annular formations. Sometimes there are coccobacillary and bacteria-like forms. Certain types of mycoplasmas (M. mycoides var. mycoides, M. mycoides var. capri, M. agalacliae) form filamentous mycelial forms in organs and nutrient media.
Electron microscopic studies and by filtering grown cultures through membrane filters with a known hole diameter showed that in the same culture there are formations of various shapes and sizes that are capable of reproduction (Fig. 1). In the study of various types of mycoplasmas isolated from the organs of animals and humans, as well as objects of the external environment, it was found that the size of elementary particles ranges from 125 to 600 im. In the determinant of Berge, the size of mycoplasma cells is estimated at 125-200 nm. According to E. Freundt, the size of the minimum reproductive units of mycoplasmas ranges between 250-300 nm. Other authors determined their size in the range of 200-500-700 nm, and G. Wildfur, using the ultrafiltration method. - 100-150 nm. It should be noted that the size of mycoplasma cells depends not only on the species and strain, but also on other factors affecting the cell.
Thus, the size of the minimum reproductive units in cultures of mycoplasmas varies considerably.
The name mycoplasma (from the Greek μυκής "mushroom" and πλάσμα "formed") was first used by Albert Bernard Frank in 1889, who considered it a fungus due to its characteristics.
Previously, mycoplasma was called a pleuropneumonia-like organism (PPLO), referring to organisms similar to the causative agent of infectious bovine pleuropneumonia (CBPP). It was later found that a similar fungal growth pattern M. mycoides is unique to this species and mycobacteria.
Video about mycoplasma
History of the study of mycoplasma
The discovery of mycoplasma dates back to 1898. The discovery and study of mycoplasma proved difficult due to its small size, difficulty in staining due to the lack of a cell wall, and the difficult laboratory conditions required for culture. Their small size means they were not originally identified as bacteria and were considered viruses for many years. Later, mycoplasmas were confused with L-forms, which are bacteria that have lost their cell walls, either completely or partially. In the 1950s and 1960s researchers began isolating and cultivating mycoplasmas and ureaplasmas, leading to their recognition as a unique genus.
Mycoplasmas are thought to have evolved from Gram-positive walled eubacteria in a degenerative evolution, meaning their evolutionary history appears to include cell wall loss and reduction in genomic data. The limited cell membrane, genome, and metabolic pathways of mycoplasmas have led to the conclusion that they are the smallest and simplest self-replicating organisms.
The absence of a cell wall is responsible for some of the unique properties of mycoplasmas, such as sensitivity to osmotic shock and detergents, resistance to penicillin and other beta-lactam antibiotics, and formation of egg-shaped colonies. On sections of mycoplasmas, one can see that their cell is essentially formed by three organelles: a cell membrane, a ribosome, and a tightly wrapped molecule with circular double-stranded DNA. Their mode of replication is no different from other prokaryotes that divide by simple nuclear fission. For binary fission to occur, cytoplasmic separation must be fully synchronized with genome replication, and in mycoplasmas, cytoplasmic replication lags behind genome replication, eventually leading to the formation of multinucleated fibers.
When grown in vitro, mycoplasmas have been found to be "fastidious", meaning they are difficult to culture. The reasons for these difficulties for species such as Mycoplasma genitalium and Mycoplasma pneumoniae, is the absence of all genes involved in the synthesis of amino acids, which makes them dependent on the exogenous supply of amino acids and other nutrients. This dependence on external supplies of fatty acids and cholesterol is an advantage for further research with these organisms. To compensate for these shortcomings, mycoplasmas are grown in complex media, usually from bovine heart extract, peptone, yeast extract, and sera with various additives.
Due to the absence of a cell wall, mycoplasmas serve as good models for membrane studies. For this reason, the presence of these membranes in their pure form allowed for their chemical, enzymatic, and antigenic characterization. The membrane consists of 60-70% protein, the remaining 20-30% are lipids.
Characteristics
Cell morphology
For bacteria of the genus Mycoplasma(trivial name: mycoplasma), like their close relatives, is characterized by the absence of a cell wall. Despite this, cells often have a definite shape, with a characteristic small size, usually about 10% of the cell volume. Escherichia coli. This shape of the cell presumably contributed to the ability of mycoplasmas to thrive in their respective environments. Most are pseudococci, but there are notable exceptions. Cluster types M. fastidiosum rod-shaped. Cluster types M. pneumoniae, including M. pneumoniae, have a polar extension protruding from the pseudococcal cell body. This tip structure, the attachment organelle or terminal organelle, is essential for attachment to host cells and for movement on hard surfaces (glide motility) and is involved in normal cell division. Cells M. pneumoniae pleomorphic, with an attachment organelle of normal size at one pole and a posterior filament of variable length and indeterminate function at the other end, while other species in the cluster generally lack a terminal filament. Other types such as M. mobile and M. pulmonis, have similar structures with similar functions.
Mycoplasmas are bacteria unusual in that most of them require sterols for the stability of their cytoplasmic membrane. They obtain sterols from the environment, usually from cholesterol from the host animal. Mycoplasmas tend to have a relatively small genome of 0.58-1.38 megabases, which results in drastically reduced biosynthetic capabilities and explains their host dependence. In addition, they use an alternative genetic code in which the UGA codon codes for the amino acid tryptophan instead of the normal stop codon. They have a low GC content (23-40 mol).
First selection
In 1898, Knockard and Roux reported the cultivation of the causative agent CBPP, which at that time was a serious and widespread disease in livestock. Illness causes M. mycoides, a mycoid subspecies SC (small colony type), and the work of Knockara and Roux represented the first isolation of mycoplasma species. Cultivation was and still is difficult due to the complex growth requirements.
These researchers were able to do this by inoculating a semi-permeable sac from a sterile environment with lung fluid from an infected animal and depositing this sac intraperitoneally into a live rabbit. After 15-20 days, the liquid inside the extracted pouch was opaque, indicating the growth of the microorganism. The opacity of the liquid was not visible in the control. This cloudy broth could then be used for the second and third rounds of inoculation, after which it was injected into a healthy animal, causing disease. However, this will not work if the material has been heated, indicating a biological agent at work. The uninoculated medium in the bag, after being removed from the rabbit, could be used to grow the organism in vitro, demonstrating the possibility of cell-free culture and ruling out viral causes, although this was not fully evaluated at the time.
small genome
Thanks to recent advances in molecular biology and genomics, a wider audience has been able to learn about genetically simple mycoplasmas, in particular, M. pneumoniae and her close relative M. genitalium. The second published complete bacterial genome sequence was M. genitalium, which has one of the smallest genomes of free-living organisms. Soon after, the genome sequence was published. M. pneumoniae and became the genome sequence, first determined using a cosmid library roaming seed instead of the whole genome shotgun method. Work continues on the genomics and proteomics of mycoplasma in an attempt to understand the so-called minimal cell in order to catalog all the protein content in the cell. In general, scientists continue to take advantage of the small genomes of these organisms to understand broad biological concepts.
Systematics
Working with family members Mycoplasma and related genera of medical and agricultural importance has led to extensive cataloging of many of these organisms through cultivation, serology, and small subunit rRNA gene and whole genome sequencing. Recent concentration in the sub-discipline of molecular phylogenetics suggests some refined and confused aspects of the organization of the mycoplasma class.
The originally trivial name "mycoplasma" usually referred to all members of this class. The name "mycoplasma" comes from the Latin mollis (soft) and cutis (skin), and all of these bacteria lack a cell wall and the genetic ability to synthesize peptidoglycan.
Despite the lack of a cell wall, many taxonomists have placed Mycoplasma and relatives in the Firmicute phylum, consisting of low G+C Gram-positive bacteria such as Clostridium, Lactobacillus and Streptococcus based on the analysis of 16S rRNA genes.
Detachment Mycoplasmatales contains one family, Mycoplasmataceae, consisting of two genera: mycoplasma and ureaplasma. Mycoplasma is now a genus of mollicutes.
Historically, the description of a bacterium lacking a cell wall was not sufficient to place it in the genus Mycoplasma, and as such it is the oldest and largest genus of the class, with almost half of the species of the class (107 described), each usually restricted to a specific host. At the same time, a large number of hosts carry several species, some pathogenic and some synanthropic. In more recent work, many of these species have been found to be distributed phylogenetically among at least three separate orders.
The limiting criterion for inclusion in the genus Mycoplasma is what organism the vertebrate host has. Indeed, a typical view M. mycoides, along with other significant mycoplasma species such as M. capricolum, evolutionarily more closely related to the genus Spiroplasma in the detachment Entomoplasmatales than with other members of the genus Mycoplasma. This and other discrepancies are likely to remain unresolved due to the extreme confusion that the changes could create among the medical and agricultural communities.
Other species of this genus Mycoplasma are divided into three non-taxonomic groups - hominis, pneumoniae and fermentans- based on 16S rRNA gene sequences.
In a group Hominis contains phylogenetic clusters M. pulmonis, M. bovis and M.hominis among others. M. hyopneumoniae is the main bacterial agent of the porcine respiratory disease complex.
Pneumonia group contains clusters M. fastidiosum,M. muris,U. urealyticum, currently uncultured hemotropic mycoplasmas, informally referred to as hemoplasmas (recently transferred from childbirth Haemobartonella and Eperythrozoon), and the cluster M. pneumoniae. This cluster contains species (and common or probable host) M. alvi(bullish), M. amphoriforme(human), M. gallisepticum(avian), M. genitalium(human), M. imitans(avian), M. pyrum(indefinite / human), M. testudinis(turtle) and M. pneumoniae(human). Most, if not all, of these species have otherwise unique characteristics, including attachment organelles, homologues of cell adhesion accessory proteins. M. pneumoniae and specialized modifications of the apparatus of cell division.
A study of 143 genes in 15 mycoplasma species suggests that the genus can be grouped into four clades: the group M. hyopneumoniae, Group M. mycoides, Group M. pneumoniae and group Bacillus-Phytoplasma. Group M. hyopneumoniae more closely associated with the group M. pneumoniae than with a group M. mycoides.
Laboratory contaminants
Mycoplasma species are often found in research laboratories as cell culture contaminants. Contamination of cell culture with mycoplasma occurs due to contamination from individuals or contaminated ingredients of the cell culture medium. Mycoplasma cells are physically small (less than 1 µm), thus difficult to detect with a conventional microscope.
Mycoplasmas can cause changes in cells, including chromosomal aberrations, changes in metabolism and cell growth. Due to severe mycoplasma infections, the cell line can be destroyed. Detection methods include DNA sampling, enzyme immunoassay, PCR, sensitive agar plating, and staining with DNA stains including DAPI or Hoechst.
It has been estimated that at least 11-15% of US laboratory cell cultures are contaminated with mycoplasma. A Corning study found that half of American scientists do not test cell cultures for mycoplasma contamination. The study also stated that in the former Czechoslovakia, 100% of the cell cultures that were not routinely tested were contaminated, while only 2% of those regularly tested were found to be contaminated. Since the contamination rate in the US was based on a study of companies that routinely test for mycoplasma, the actual contamination rate may be higher. The percentage of contamination is higher in Europe and even higher in other countries (up to 80% of cell cultures in Japan). Perhaps about 1% of the published Gene Expression Omnibus data has been discredited. Over the years, several antibiotics have been developed based on the anti-mycoplasma reagent formula.
Synthetic mycoplasma genome
The chemically synthesized genome of a mycoplasmal cell, based entirely on synthetic DNA that can reproduce itself, is called Mycoplasma Laboratorium.
pathogenicity
Several types of mycoplasmas are capable of causing disease, including M. pneumoniae, which is an important cause of SARS (formerly known as "walking pneumonia"), and M. genitalium, which has been associated with pelvic inflammatory disease. infections Mycoplasma in humans are associated with skin rashes in 17% of cases.
Virulence factor
The P1 antigen is the main virulence factor of mycobacteria. P1 is a membrane-associated protein that allows adhesion to epithelial cells. The P1 receptor is also expressed on erythrocytes, which can lead to agglutination of autoantibodies from mycobacterial infection.
Association with cancer
Several types of mycoplasma are often found in various types of cancer cells, these are:
- M. fermentans
- M. genitalium
- M. hyorhinis
- M. penetrans
Most of these mycoplasmas showed a strong correlation with malignant transformation in mammalian cells in vitro.
Mycoplasma infection and host cell transformation
The presence of mycoplasma in tumor tissue samples was first reported in the 1960s. Since then, several studies have been carried out in an attempt to find and prove the connection between mycoplasma and cancer, as well as how the bacterium may be involved in the formation of cancer. Some studies have shown that cells that are chronically infected with bacteria go through a multi-step transformation. Changes caused by chronic mycoplasmal infections occur gradually and are both morphological and genetic. The first visual sign of infection is when the normal shape of the cells gradually changes to crescent. They also become hyperchromic due to the increase in DNA in the cell nuclei. In later stages, cells lose their need for a solid carrier in order to grow and multiply.
Possible intracellular mechanisms of mycoplasmal malignant transformation
Significant chromosomal abnormalities occur in cells infected with mycoplasma over a long period of time. They include addition of chromosomes, loss of whole chromosomes, partial loss of chromosomes, and chromosomal translocations. All of these genetic abnormalities can contribute to the process of malignant transformation. Chromosomal translocation and extra chromosomes help in creating abnormally high activity of some proto-oncogenes. Proto-oncogenes with increased activity due to these genetic abnormalities include those encoding c-myc, HRAS, and vav. Proto-oncogene activity is not the only affected cellular function. Tumor suppressor genes are also affected by chromosomal changes caused by mycoplasma. Partial or complete loss of chromosomes leads to the loss of important genes involved in the regulation of cell proliferation. Two genes that are markedly downregulated during chronic mycoplasma infections are Rb and the p53 tumor suppressor genes. Another possible mechanism of carcinogenesis is the activation of RAC1 by a small GTP-like fragment protein Mycoplasma. The main feature that distinguishes mycoplasma from other carcinogenic pathogens is that it does not cause cellular changes by introducing its own genetic material into the host cell. The exact mechanism by which the bacterium causes the changes is not yet known.
Partial reversibility of malignant transformations
Malignant transformation induced by mycoplasma also differs from that induced by other pathogens in that the process is reversible. The state of reversibility, however, is only possible up to a certain point during the infection. The length of time during which reversibility is possible varies greatly and depends primarily on the mycoplasma involved. When M. fermentans the transformation is not reversible until about the 11th week of infection and becomes irreversible between the 11th and 18th weeks. If the bacteria are killed by antibiotics (such as ciprofloxacin or clarithromycin) to an irreversible stage, the infected cells should return to normal.
Association with in vivo cancer and future research
Although mycoplasmas have been confirmed to be carcinogenic in vitro, it has not yet been confirmed whether they can be the actual cause of cancer in vivo. Recently, however, epidemiological, molecular and genetic studies have shown that infection and inflammation initiate some cancers, including those of the prostate. A 2009 study found that Mycoplasma genitalium and Mycoplasma hyorhinis induce a malignant phenotype in benign human prostate cells (BPH-1) that were "non-oncogenic" 19 weeks after exposure. This study is described as one of the first reports describing the ability M. genitalium or infection M. hyorhinis lead to malignant transformation in benign human epithelial cells.
Some of the uncertainty about the potential of bacteria to cause malignant tumors is potentially related to the fact that the cells used in research are often derived from an immortalized cell line, such as BEAS-2b cells. They are essentially cells on the verge of becoming cancerous. One of the problems with using such cells to induce carcinogenesis is that they convert spontaneously after 32 passes (when a small number of cells are transferred to a new vessel to prolong the culture). This, and the fact that malignant transformation was not directly detected in non-immortalized "normal" cells that were infected, may mean that mycoplasma accelerates cell progression to malignancy, but is not the cause. In vivo cultures, the presence of mycoplasma-generated cancer has not yet been documented. However, it may be that very long, chronic mycoplasma infections can cause cancer in non-immortalized cells. This is not yet known, since non-immortalized cells can only divide for a limited amount of time, and so it has not been possible to keep culturing them long enough to start cancer. More research is needed to confirm that mycoplasma infections cause cancer or initiate malignant tumors in human cells. This could be an important step in the treatment and prevention of cancer.
Cancer types associated with mycoplasma
- colon cancer: In a study that attempted to understand the effects of mycoplasma contamination on the quality of cultured human colon cancer cells, a positive correlation was found between the number M. hyorhinis in the sample and the percentage of CD133 (glycoprotein of unknown function) positive cells. Further testing and analysis should determine the exact cause of this phenomenon.
- Stomach cancer: There are signs that the infection M. hyorhinis contributes to the development of cancer in the stomach and increases the likelihood of developing a malignant cancer cell.
- Lungs' cancer: Lung cancer studies support the belief that there is a non-random positive correlation between the occurrence of strains Mycoplasma in patients and tumorigenesis infection. Since this is a new area of research, more research is needed to further understand their relationship and identify possible preventive measures for lung cancers involving mycoplasma.
- prostate cancer: p37, protein encoded for M. hyorhinis has been found to promote invasiveness of prostate cancer cells. The protein also induces growth, morphology, and gene expression in the cells to be changed, resulting in a more aggressive phenotype.
- kidney cancer: Patients with renal cell carcinoma (RCC) have significantly higher numbers of Mycoplasma sp. compared to a healthy control group. This suggests that mycoplasmas may play a role in the development of RCC.
Mycoplasmas are tiny particles. They are the smallest self-replicating prokaryotes. The morphology and size of mycoplasmas vary depending on the age of the culture, conditions and culture media. Mycoplasmas are polymorphic. Mycoplasma cells are limited only by a three-layer plasma membrane (intraplasmic membranes were not found in mycoplasmas). In 1935, filterable, cell wallless forms were isolated from the bacteria Streptobacillus moniliformis, which remarkably resembled mycoplasmas. Recently, they have been called L-forms of bacteria. The state of the L-form is due to the influence of adverse environmental factors (for example, the use of antibiotics that act on the cell wall). In their absence, the L-form is reversible. In mycoplasmas, unlike other bacteria, the state of the L-form, i.e. the absence of a cell wall is their usual state.
The absence of a cell wall in mycoplasmas determines their plasticity, which allows these microorganisms to penetrate through the pores of filters with a diameter of 0.22 - 0.45 microns. Due to the filterability of mycoplasmas, they have long been confused with viruses. The spherical shape of the cells is characteristic of most types of mycoplasmas. At the same time, cells of the same mycoplasma can be spherical (or somewhat elongated) 0.3–0.8 µm in diameter, but can form long (up to 100 µm), sometimes branching strands, which, passing through the phase of coccoid structures, disintegrate into a number of spherical cells, which is shown in Figure 2. Coccoid structures sometimes form a ring.
Mycoplasmas do not form so-called resting forms or spores. Like other non-spore-forming bacteria, mycoplasmas become unculturable under unfavorable conditions, and also form "minimal bodies" that are not capable of reproduction, since they probably do not contain DNA.
Figure 2
a) - morphological transformations under optimal cultivation conditions in vitro
b) - morphological forms under suboptimal conditions, at the stationary phase of culture growth
Some types of mycoplasmas have sliding mobility. The cells of such mycoplasmas have special structures and cytoskeleton-like formations. Thus, M. gallisepticum cells are pear-shaped, M. pneumoniae are also pear-shaped, but more elongated, and M. mycoides are more often cord-shaped.
The cells of most bacteria can be covered with a shell - a polymeric substance that has many properties and functions. This shell, or capsule, is different from the two-layer membrane and is located above it. In bacteria, the term "capsule" is used to refer to the high molecular weight polymers that "attach" to the surface of the bacteria. Although the peptidoglycan cell wall, which is characteristic of most prokaryotes, is absent in representatives of the Mollicutes class, capsules or capsule-like structures have been described for some types of mycoplasmas. They are possessed by Mycoplasma mycoides, M. gallisepticum, M. hyopneumoniae, M. meleagridis, M. dispar, M. pneumoniae, M. pulmonis, M. synoviae, M. hominis. Among ureaplasmas, only some strains of Ureaplasma urealitycum are able to form capsules.
Human diseases caused by mycoplasmas are grouped into the group of mycoplasmoses. These are anthroponotic bacterial infections caused by mycoplasmas that affect, depending on the type of pathogen, the respiratory or genitourinary tract and rarely other organs.
The causative agents of this group of infections - mycoplasmas are the smallest free-living bacteria. The average size of their cells is 0.27-0.74 microns. They attract a lot of attention from researchers for two reasons:
Because of its unique organization;
Due to the fact that very often they contaminate cell cultures, cause diseases of plants, animals and humans, have
influence on the reproduction of a number of viruses, including oncogenic and HIV, and are themselves capable of causing immunodeficiencies.
Mycoplasmas belong to the class Mollicutes, which includes 3 orders (Fig. 16.2): Acholeplasmatales, Mycoplasmatales, Anaeroplasmatales. Order Acholeplasmatales includes family Acholeplasmataceae with a single gender Acholeplasma. Order Mycoplasmatales consists of 2 families: Spiroplasmataceae with a single gender Spiroplasma and mycoplasmataceae, including 2 kinds: Mycoplasma and Ureaplasma. Newly allocated order Anaeroplasmatales consists of a family anaeroplasmataceae, including 3 kinds: Anaeroplasma, Asteroplasma, Termoplasma. The term "mycoplasmas" usually refers to all microbes of the families Mycoplasmataceae and Acholeplasmataceae.
Morphology. A distinctive feature is the absence of a rigid cell wall and its precursors, which determines a number of biological properties: cell polymorphism, plasticity, osmotic sensitivity, the ability to pass through pores with a diameter of 0.22 μm, resistance to various agents that inhibit cell wall synthesis, including penicillin and its derivatives, the multiplicity of reproduction pathways (binary fission, budding, fragmentation of threads, chain forms and spherical formations). Cells 0.1-1.2 microns in size, gram-negative, but better stained according to Romanovsky-Giemsa; Distinguish between movable and immovable types. The minimal reproducing unit is the elementary body (0.7-0.2 microns) spherical or oval, later elongating up to branched filaments. The cell membrane is in the liquid crystal
thallic state; includes proteins mosaically immersed in two lipid layers, the main component of which is cholesterol. The genome size is the smallest among prokaryotes (1/16 of the rickettsia genome); have a minimal set of organelles (nucleoid, cytoplasmic membrane, ribosomes). The ratio of GC-pairs in DNA in most species is low (25-30 mol.%), with the exception of M. pneumoniae(39-40 mol.%). The theoretical minimum content of HC required for coding proteins with a normal set of amino acids is 26%, therefore, mycoplasmas are located at this edge. The simplicity of organization, the limitedness of the genome determine the limitations of their biosynthetic capabilities.
cultural properties. Chemoorganotrophs, most species have a fermentative metabolism; the main source of energy is glucose or arginine. Grow at a temperature of 22-41 "C (optimum - 36-37 ° C); optimum pH - 6.8-7.4. Most species are facultative anaerobes; extremely demanding on nutrient media and cultivation conditions. Nutrient media must contain all precursors necessary for the synthesis of macromolecules, to provide mycoplasmas with energy sources, cholesterol, its derivatives and fatty acids.For this, beef heart and brain extract, yeast extract, peptone, DNA, NAD are used as a source of purines and pyrimidines, which mycoplasmas cannot synthesize. the following are introduced into the medium: glucose - for species that ferment it, urea - for ureaplasmas and arginine - for species that do not ferment glucose.The source of phospholipids and styrenes is the blood serum of animals, for most mycoplasmas - the blood serum of a horse.
The osmotic pressure of the medium should be in the range of 10-14 kgf/cm 2 (the optimal value is 7.6 kgf/cm 2), which is ensured by the introduction of K + and Na + ions. Glucose-fermenting species grow better at lower pH values (6.0-6.5). Aeration requirements vary from species to species, most species grow best in an atmosphere of 95% nitrogen and 5% carbon dioxide.
Mycoplasmas are cultivated on liquid, semi-liquid and dense nutrient media. Some types, for example M. pneumoniae, can be cultured on glass or plastic as a monolayer, like cell cultures. Most species reproduce slowly, cultivating for days or even weeks. (M. pneunoniae, M. genitalium). M.hominis reaches the beginning of the stationary phase of growth only after 48-72 hours, the titer of the culture is 10 7 -10 8 CFU / ml, this titer is maintained in the stationary phase of growth for 5-7 days of cultivation. Ureaplasmas have a very short stationary phase, their viability drops sharply after 24 hours, when approximately 90% of the cells die, especially in a poorly buffered medium. Broth cultures of mycoplasmas are slightly opalescent; ureaplasmas do not cause turbidity of the medium even at a titer of 10 7 CFU/ml. In the thickness of the semi-liquid agar, mycoplasmas and ureaplasmas form a light cloud along the pipette injection, visible in transmitted light. On dense media, mycoplasmas form characteristic small colonies (0.1–0.3 mm) with a raised center (“fried eggs”), which tend to grow into the medium and have a delicate, often openwork periphery; ureaplasmas form very small colonies (0.01-0.03 mm in diameter). Growth is inhibited by specific immune sera.
Chicken embryos are suitable for cultivation, which die after 3-5 passages.
The biological properties of mycoplasmas isolated from humans are presented in Table. 16.38.
biochemical activity. Low. There are 2 groups of mycoplasmas:
Decomposing with the formation of acid glucose, maltose, mannose, fructose, starch and glycogen ("true" mycoplasmas);
Reducing compounds of tetrazolium, oxidizing glutamate and lactate, but not fermenting carbohydrates.
All species do not hydrolyze urea and esculin. The main biochemical properties of pathogenic mycoplasmas are presented in Table. 16.39.
* a. y. - aerobic conditions.
** an. y. - anaerobic conditions.
Ureaplasmas are inert to sugars, do not restore diazadyes, are catalase-negative; show p-hemolytic activity to rabbit and guinea pig erythrocytes; produce hypoxanthine. Ureaplasmas secrete phospholipases A1, A2 and C; proteases that selectively act on IgA molecules and urease. A distinctive feature of the metabo-
lysma - the ability to produce saturated and unsaturated fatty acids.
Antigenic structure. Complex, has specific differences; the main AGs are represented by phospho- and glycolipids, polysaccharides and proteins; The most immunogenic are superficial AGs, which include carbohydrates as part of complex glycolipid, lipoglycan, and glycoprotein complexes. The antigenic structure can change after repeated
passages on cell-free nutrient media. A pronounced antigenic polymorphism with a high frequency of mutations is characteristic.
M. hominis the membrane contains 9 integral hydrophobic proteins, of which only 2 are more or less constantly present in all strains.
In ureaplasma, 16 serovars are isolated, divided into 2 groups (A and B); the main antigenic determinants are surface polypeptides.
pathogenicity factors. Diverse and can vary significantly; the main factors are adhesins, toxins, aggression enzymes and metabolic products. Adhesins are part of surface antigens and cause adhesion on host cells, which is of key importance in the development of the initial phase of the infectious process. Exotoxins have so far been identified only in a few non-pathogenic mycoplasmas, in particular in M. neurolyticum and M. gallisepticum; targets for their action are the membranes of astrocytes. Suggested presence of neurotoxin in some strains M. pneumoniae, as often respiratory tract infections accompany lesions of the nervous system. Endotoxins have been isolated from many pathogenic mycoplasmas; their introduction to laboratory animals causes a pyrogenic effect, leukopenia, hemorrhagic lesions, collapse and pulmonary edema. In their structure and some properties, they are somewhat different from LPS Gram-negative bacteria. In some species, hemolysins are found (the highest hemolytic activity possesses M. pneumoniae); most species cause pronounced (3-hemolysis due to the synthesis of free oxygen radicals. Presumably, mycoplasmas not only synthesize free oxygen radicals themselves, but also induce their formation in cells, which leads to the oxidation of membrane lipids. Among the aggression enzymes, the main pathogenicity factors are phospholipase A and aminopeptidases that hydrolyze phospholipids of the cell membrane Many mycoplasmas synthesize neuraminidase, which interacts with the surface structures of the cell containing sialic acids;
enzyme activity disrupts the architectonics of cell membranes and intercellular interactions. Among other enzymes, we should mention proteases that cause degranulation of cells, including mast cells, cleavage of AT molecules and essential amino acids, RNases, DNases, and thymidine kinases that disrupt the metabolism of nucleic acids in body cells. Up to 20% of the total DNase activity is concentrated in the membranes of mycoplasmas, which facilitates the intervention of the enzyme in cell metabolism. Some mycoplasmas (eg. M. hominis) synthesize endopeptidases that cleave IgA molecules into intact monomeric complexes.
Sustainability in the environment. Low, especially in "urogenital mycoplasmas". Mycoplasmas and ureaplasmas are sensitive to fluoroquinolones, macrolides, cephalosporins, azalides and tetracyclines; 10% of ureaplasmas are resistant to tetracyclines and macrolides. Sensitive to commonly used antiseptics and disinfectants.
Epidemiology. Mycoplasmas are widely distributed in nature. Currently, about 100 species are known, they are found in plants, mollusks, insects, fish, birds, mammals, some are part of the microbial associations of the human body. From a person, 15 types of mycoplasmas are isolated; their list and biological properties are given in table. 16.38. A.ladlawii and M. primatum rarely isolated from humans; 6 kinds: M. pneunoniae, M. hominis, M. genitalium, M. fermentans (incognitis), M. penetrans and U. urealyticum have potential pathogenicity. M. pneumoniae colonizes the mucous membrane of the respiratory tract; M. hominis, M. genitalium and U. urealyticum- "urogenital mycoplasmas" - live in the urogenital tract.
The source of infection is a sick person. The transmission mechanism is aerogenic, the main route of transmission is airborne; susceptibility is high. The most susceptible are children and adolescents aged 5-15 years. The incidence in the population does not exceed 4%, but in closed groups, for example, in military formations, it can reach 45%. The peak incidence is the end of summer and the first autumn months.
The source of infection is a sick person; ureaplasmas infect 25-80% of people who are sexually active and have three or more partners. Transmission mechanism - contact; the main route of transmission is sexual, on the basis of which the disease is included in the STD group; susceptibility is high. The main risk groups are prostitutes and homosexuals; ureaplasma is much more often detected in patients with gonorrhea, trichomoniasis, candidiasis.
Clinic. Respiratory mycoplasmosis can occur in the form of a limited infection of the upper respiratory tract (nasopharyngitis) or by the type of bronchitis or pneumonia, as well as various extrarespiratory manifestations associated with the generalization of the infectious process, the development of autoimmune reactions and impaired hemocirculation. M. pneumoniae- one of the main causative agents of pulmonary lesions, causes up to 20% of all pneumonias. Pneumonias proceed according to the type of interstitial and focal lesions; rarely observe segmental, lobar or
mixed pneumonia. In severe cases, pleurisy develops. Extra-respiratory manifestations: hemolytic anemia, neurological disorders (meningitis, lesions of the peripheral CNS and cranial nerves), complications from the cardiovascular system (myocarditis) and the musculoskeletal system (reactive arthritis, spondylitis, rheumatoid arthritis).
"Urogenital mycoplasmas" cause acute, but more often chronic GI infections of the genitourinary tract. Their role in the development of non-gonococcal urethritis, spontaneous abortions, premature births, habitual miscarriage, the birth of children with low body weight and malformations, infertility in men and women has been proven. At the same time, mycoplasmosis is not always an indicator of a pathological process. The state of the immune system, the physiological state and hormonal background of a person, the presence of other concomitant infections can contribute to the activation of the reproduction of "urogenital mycoplasmas" and the development of a clinically pronounced pathological process.
Immunity. The development of the immune response is not accompanied by the formation of specific resistance; cases of re-infection are typical for respiratory and urogenital mycoplasmosis. Phagocytosis is incomplete, in the absence of AT, macrophages are not able to phagocytize mycoplasmas, which is due to the presence of microcapsules, surface antigens that cross-react with antigens of some tissues of the human body (lungs, liver, brain, pancreas, smooth muscles and erythrocytes).
In the cytoplasm of neutrophils, the pathogen retains its viability. Mycoplasmas are sensitive to complement components, their deficiency or defects create conditions for the persistence of the pathogen. Short-lived IgA determine the elimination of the pathogen from the mucous membranes; polyclonal stimulation of lymphocytes leads to the formation of infiltrates in the lung tissue, the appearance of cross-reacting antibodies and the development of DTH. Mycoplasmosis is characterized by the development of autoimmune reactions. Infection M. fermentans accompanied by the formation of AT to IgG (due to the binding of Fc fragments), i.e., the rheumatoid factor involved in cell damage. Damage to articular tissues is induced by AT that cross-reacts with tissue AG.
it of the body in case of damage to the integrity of the cartilage tissue and the exposure of "hidden" cellular AG.
Microbiological diagnostics. If respiratory mycoplasmosis is suspected, smears from the nasopharynx, lavage fluid, sputum, bronchial lavage, as well as smears-imprints of tissues of organs of stillborn and aborted fetuses are examined. In case of urogenital infections, the middle portion of morning urine, scrapings from the mucous membrane of the urethra, vaginal vaults, cervical canal, material obtained during laparoscopy, amniocentesis, smears-imprints of tissues of organs of stillborn and aborted fetuses are examined. With prostatitis, the secret of the prostate is examined, with male infertility - sperm. When taking the material, the same rules are observed as in the study for chlamydia.
For laboratory diagnosis of mycoplasmal infections, culipural, serological and molecular genetic methods(Table 16.40):
In serodiagnosis, smears-imprints of tissues, scrapings from the urethra, cervical canal and vagina, prostate secretion and sperm, in which mycoplasma AG can be detected in direct and indirect RIF, serve as the material for research. Mycoplasmas and ureaplasmas stain bright green and are detected on the surface of the analyzed cells in the form of green granules arranged in groups or singly, colored green granules can be located in the non-cellular space. The cytoplasm of cells is stained red-brown. The result is considered positive if at least 10 luminous green granules located on the cell membrane are found in the preparation.
AG mycoplasmas can also be detected in the blood serum of patients. To do this, use the reaction of aggregate-hemagglutination (RAGA) and ELISA.
The peculiarity of RAGA is that for the sensitization of erythrocytes, immune serum proteins aggregated with glutaraldehyde are used, while AT are introduced into three-dimensional protein complexes, as a result of which part of the AT active centers move away from the surface of the erythrocyte and become more accessible to AH determinants.
For serodiagnosis of respiratory mycoplasmosis, specific antibodies are determined in paired sera of the patient; seroconversion of 4 times or more is of diagnostic value. The determination of AT in urogenital infections is of less diagnostic value, since the infection, as a rule, has a chronic course, and "urogenital mycoplasmas" are weak antigenic stimuli. Nevertheless, in urogenital mycoplasmoses, serodiagnosis is carried out in some cases, AT is most often determined in RPHA and ELISA.
Molecular biological diagnostic methods include hybridization based on DNA probes and PCR. The first method allows the identification of mycoplasma species in the presence of 10,000-100,000 cells per sample. PCR allows you to identify single cells of mycoplasmas.
Treatment. Antibiotics. Directed etiotropic chemotherapy usually gives a good effect, but the disappearance of clinical symptoms often does not mean complete elimination of the pathogen.
Prevention. There is no specific prophylaxis. Non-specific prophylaxis is aimed at eliminating the source of infection; to break the mechanism and transmission routes; as well as to increase the immunity of the collective to infection.
Ministry of Education and Science of the Russian Federation
Federal State Budgetary Educational Institution
Higher professional education
"Ufa State Oil Technical University"
Department of Biochemistry and Technology of Microbiological Production
Course work
in the discipline "General biology and microbiology"
Mycoplasmas: representatives, structural and metabolic features, taxonomy
Fulfilled Art. gr. BTB-14-02 A.S. Kuznetsova
Checked by teacher A.N. furriers
Norm control F.A. Prishchepov
Introduction
2. Main representatives
4. Systematics
Conclusion
Introduction
Despite their very small size and very fragile membrane, these microorganisms reproduce successfully in the human body. Mycoplasmas can be present in the soil, on flora, and even in some warm underground sources, but their full life cycle can take place exclusively in human tissues (or tissues of the animal body).
Human diseases caused by mycoplasmas are grouped into the group of mycoplasmoses. The causative agents of mycoplasmosis - mycoplasmas - are the smallest, free-living prokaryotes. Unlike the L-forms of bacteria, the absence of a cell wall in mycoplasmas is an irreversible condition.
1. General information about mycoplasmas
Mycoplasmas are microorganisms that occupy an intermediate position between bacteria, fungi and viruses. These are the smallest organisms that exist in nature, differing from bacteria in their small size (150-450 nm) and the absence of a true cell membrane, capable of living and reproducing independently (Figure 1).
Figure 1 - Shape of mycoplasmas
According to modern classification, they belong to the Mycoplasmataceae family. Representatives of the mycoplasma group (class Mollicutes) are the smallest prokaryotes that can reproduce on their own. Because the protoplast is externally limited only by the plasma membrane, the cells are extremely osmotically labile.
In most mycoplasmas, the genome is 4 times smaller than in Escherichia coli, thus, among prokaryotes capable of independent reproduction, they have the smallest genome.
The order Mycoplasmatales was singled out as a separate class of bacteria, emphasizing the phylogenetic difference of mycoplasmas from all other bacteria.
2. Main representatives
Up to fourteen varieties of mycoplasmas can be found in the human body. In this case, diseases are provoked only by some of them:
Mycoplasma salivarium and Mycoplasma orale are common oral microorganisms that are unable to cause disease.
Mycoplasma pneumoniae is a microorganism that causes an atypical form of pneumonia, as well as mycoplasmal bronchitis (pulmonary mycoplasmosis) in patients of any age.
Mycoplasma hominis is always present in the urinary and reproductive organs. There is evidence that this type of pathogen causes urogenital mycoplasmosis.
Mycoplasma fermentans, Mycoplasma genitalium, and Mycoplasma penetrans also inhabit many of the mucous membranes of the human body. However, there is no data on their pathogenicity.
Mycoplasmas are small bacteria surrounded by a cytoplasmic membrane and do not have a cell wall, instead of which they are covered with a three-layer membrane. Thanks to this, mycoplasmas can change shape and even pass through bacterial filters.
Mycoplasmas are resistant to sulfonamides, penicillin, streptomycin, cell wall synthesis inhibitors, protein synthesis inhibitors, nucleic acid synthesis inhibitors, Beta-lactams, but are sensitive to tetracycline antibiotics, macrolides, and fluoroquinolones.
Mycoplasmas quickly die when boiled, ultraviolet irradiation and exposure to disinfectants. Different species are either strict aerobes or obligate anaerobes.
"Atypical" mycoplasmas means:
Lack of peptidoglycan.
Filterability.
The disease is caused either by a weakening of the host's immune system, or by a combination of pathogenic types of mycoplasma with other pathogenic microorganisms.
It is transmitted from person to person by airborne droplets with droplets of sputum and saliva released by patients during coughing. The spread of microbes occurs by contact with things contaminated with sputum or saliva. Mycoplasma infection is manifested by sinusitis, pharyngitis, bronchitis, pneumonia.
If mycoplasmosis affects the genitourinary system, then it is referred to as a sexually transmitted disease caused by microorganisms Mycoplasma hominis. Mycoplasmas can be present in the body of perfectly healthy people without manifesting themselves, but under certain conditions they can contribute to the development of a number of diseases, such as uregonal mycoplasmosis.
It is still not fully understood how Mycoplasma hominis attaches to epithelial cells. It is known that this bond is quite strong, but complete attachment to the cell, as is the case with many viruses, does not occur. A strong connection with the host is provided by several factors: the similarity of the structure of the mycoplasma cell membrane with the membranes of the host organism, the absence of a cell wall, and the small size of mycoplasmas.
In addition, the introduction of mycoplasmas into the membrane of host cells makes them more protected from the effects of the host's immune system. Cultivated on serum agar with the addition of thallium acetate to suppress foreign flora. On a dense nutrient medium, mycoplasmas form colonies resembling scrambled eggs: an opaque central part and a periphery immersed in the medium and translucent in the form of a circle.
2.2 Prevalence and methods of control
Mycoplasmas are able to grow on a wide range of media: from simple mineral to complex organic, some - only in the host organism. Mycoplasma metabolic products (peroxides, nucleases, hemolysins) have a destructive effect on the host cell.
Mycoplasmas are unstable to the external environment - they quickly die outside the host organism, therefore infection with mycoplasmas occurs, as a rule, either sexually or through close household contacts.
Domestic infection occurs through personal hygiene items (linen, swimwear, towels, bedding). Possible vertical transmission of mycoplasmosis - transmission of mycoplasmosis during childbirth. In this way, newborn girls are more likely to become infected, which is associated with the characteristics of their body.
Another source of infection is a person with a manifest or asymptomatic course of mycoplasmosis. The infection is transmitted by airborne droplets (with respiratory mycoplasmosis), sexual (with urogenital mycoplasmosis) and vertical (from mother to fetus - more often with urogenital mycoplasmosis) routes.
The duration of the latent period of the disease is from 3 days to 5 weeks, on average 15-19 days.
More often, mycoplasma infections are found in association with other microorganisms, such as trichomonas, gardnerella, chlamydia, fungi, and herpes simplex virus.
Due to the fact that mycoplasmas are small and located inside infected cells, they are not affected by cells of the immune system and antibodies.
Microbes are very mobile, when one cell is destroyed, they move to other cells, infecting them. They are firmly attached to the cell walls, this allows the infection to penetrate into the body with the very minimum amount. Active multiplication of microbes in the lining surface of the bronchi and trachea immediately stops the functions of the cells.
Mycoplasmas cause the chronic course of mycoplasmosis due to their structural similarity to some components of normal tissues of the human body. Due to the difficulty of recognizing these microorganisms by the patient's immune system, their long-term survival in infected tissues is observed.
Treatment of mycoplasmosis of the genitourinary system is carried out by a venereologist. Identification of the pathogen is possible with the help of the analysis of sowing on nutrient media. The establishment of the type of microbes is carried out by the method of enzyme immunoassay (PIF) or by the polymerase chain reaction (PCR).
Therapeutic treatment of mycoplasmosis should be correct, take place only under medical supervision, because any inflammatory processes are fraught with complex consequences. The main complex necessarily consists of antibacterial drugs prescribed by the attending physician to each patient individually. Due to the fact that mycoplasmas can show resistance to some antibiotics, self-medication is unacceptable.
There are no special measures that could help avoid infection with mycoplasma. The main warnings are:
intimate relationship with only one person who also has no other partners except you
use of condoms, visits to the gynecologist once every six months
if a pathogen is detected, immediate treatment under the supervision of a doctor.
In plants, mycoplasmas are the causative agents of etiolation diseases. They are predominantly localized in the phloem and, due to their external resemblance to spirilla, are united in the genus Spiroplasma. Spiroplasma has also been found in bees and grasshoppers. One might think that insects serve not only as vectors but also as hosts for Spiroplasma species.
Factors that determine the dependence of mycoplasmas on the host cell:
Demand for ready-made sterols.
Inability to synthesize ATP.
Absence of ribosomes.
Inability to synthesize DNA.
3. Features of the structure and metabolism
Mycoplasmas are not capable of biosynthesis of fatty acids, amino acids, purines and pyrimidines. There are no clear ideas about how to obtain energy in mycoplasma cells.
All studied mycoplasmas have "truncated" airways. They lack a full cycle of tricarboxylic acids, quinones and cytochromes. This means that the chain of metabolic reactions, during which electrons are transferred from the substrate to oxygen and energy is converted into ATP, terminates at flavins. Meanwhile, a significant increase in potential occurs precisely at the stages associated with cytochromes.
Therefore, unlike organisms with a complete respiratory chain, the energy potential of mycoplasmas should theoretically be much less.
Indeed, it has been experimentally shown that the percentage of ATP among adenylates in the cells of the studied representatives of the genera Acholeplasma and Mycoplasma is only 45-63.
Thus, in the exponential phase of growth, mycoplasma cells experience significant energy deficiency.
Probably, this deficiency can be compensated by the presence of other enzymes, mainly nucleases, proteases, and transport systems, with the help of which mycoplasmas are able to extract the necessary compounds from the cells of higher eukaryotes.
Mycoplasmas have a fairly pronounced enzymatic activity.
The ability to degrade certain compounds is used to differentiate mycoplasmas. The main compound that mycoplasmas use for energy is arginine or glucose, some species have the ability to break down both compounds.
Mycoplasmas are also distinguished by some other features (Figure 2).
Figure 2 - Differential characters of the genus Mycoplasma.
Mycoplasmas are chemoorganotrophs. Metabolism in most of the studied species is fermentative. Most species are facultative anaerobes.
Bacterial forms that are morphologically (formally) similar to mycoplasmas are: plasmids, spores, L-forms, protoplasts, spheroplasts.
Mycoplasmas grow on artificial nutrient media, but they need cholesterol, long-chain fatty acids and some other compounds, the need for which is satisfied by adding mammalian serum to the nutrient medium. Mycoplasmas also grow on liquid and semi-solid (1-1.3% agar) media.
On agar media, characteristic colonies are formed, growing with the central part into the nutrient medium. The type of colonies resembles scrambled eggs - fried eggs. The optimal pH value of nutrient media for most species is 7 - 7.5, for Ureaplasma urealyticum - 6.5, which is a hallmark of this genus of mycoplasmas.
Reproduction of mycoplasmas occurs through the development of small coccoid structures (elementary bodies) in the filaments with their subsequent release after the destruction of the filaments, as well as binary fission, a process similar to budding, fragmentation of large bodies and filaments.
The absence of a cell wall entailed a number of morphological, cultural, cytological features inherent in these microorganisms. They are characterized by pronounced polymorphism. In a culture of one species, one can simultaneously detect large spherical bodies, small grains, cells of an elliptical, disc-shaped, rod-shaped and filamentous shape. The latter can branch, forming structures similar to mycelial ones (Figure 3).
Figure 3 - The structure of mycoplasma
In terms of the amount of genetic information contained in the genome, mycoplasmas occupy an intermediate position between Escherichia coli and T-phages.
Energy metabolism of the enzymatic or oxidative type. Glucose utilization occurs via the glycolytic pathway.
In mycoplasmas that carry out the complete oxidation of the energy substrate, a functioning TCA and an electron carrier chain have been found.
Mycoplasmas in their composition and features reflect:
Genetic relationship of mycoplasmas with fungi.
The genetic proximity of mycoplasmas to actinomycetes.
Genetic relationship of mycoplasmas with mycobacteria.
One of the morphological features of mycoplasmas.
Formation of a moldy film during growth.
The interaction of mycoplasmas with the immune system can lead to the development of deep pathological processes in the body. Mycoplasmas have the ability to immunomodulate and can both stimulate and suppress the response of the immune system.
4. Systematics
4.1 Taxonomy: general information
The initial principles for the classification of mycoplasmas were formulated in the works of Edward and Freund. Later, the classification was changed in connection with the description of new species and the establishment of their relationship with taxa of the class Mollicutes.
Mycoplasmas belong to the Tenericutes division of the kingdom Prokaruota. The Tenericutes division is represented by one class, Mollicutes.
The class Mollicutes ("soft-skinned") includes mycoplasmas. There are three orders in the class Mollicutes - Mycoplasmatales, Acholeplasmatales and Anaeroplasmatales. In the order Mycoplasmatales, there are families - Mycoplasmataceae, Entomoplasmataceae and Spiroplasmataceae. Only the family Mycoplasmataceae has medical significance, containing two genera - the genus Mycoplasma and the genus Ureaplasma. In general, the genus Mycoplasma includes about 100 species, and in the genus Ureaplasma there are only 3 species.
For a long time, mycoplasmas were classified according to the etiological principle, based on their relationship with the host organism, which is reflected in the Latin names of many mycoplasmas: Mycoplasma hyorhinis and Mycoplasma hyopneumoniae cause rhinitis and pneumonia in pigs; Mycoplasma bovis and Mycoplasma hominis were initially found in cattle and humans, respectively.
#"center"> 4.2 Taxonomy: phylogenetic approach
Ideally, taxonomy should be based on phylogeny data, reflecting the features of the evolution of organisms and speciation. The construction of new phylogenetic trees became possible due to the development of molecular biology.
Since the 1980s, molecular genetic methods have been used to solve the problems of phylogeny and taxonomy of microorganisms: DNA hybridization, electrophoretic analysis (DNA restriction spectra) and polymerase chain reaction (PCR).
As a result of the analysis of the nucleotide sequences of mycoplasma genomes, it was found that all representatives of the Mollicutes class are characterized by genetic heterogeneity and pronounced genome instability. The rRNA genes are the only regions of extended homology of the genomes of some mycoplasma species belonging to the same genus. In the taxonomy of microorganisms, it is accepted that a species in bacteria can combine strains that have at least 70% DNA homology. A comparative analysis of the complete genomic sequences of bacterial strains will undoubtedly be more informative for the classification of microorganisms, including for the separation of taxa, than a simple (and not very accurate) determination of the percentage of DNA homology based on the results of hybridization analysis.
Conclusion
Mycoplasmas are classified as opportunistic pathogens that cause mainly latent infections. These infections are characterized by a chronic course, and the disappearance of symptoms of infection does not mean the elimination of mycoplasmas from the body. The consequence of mycoplasma infection is often a long-term (and sometimes lifelong) persistence of mycoplasmas in the body.
Mycoplasma infections can be an indicator of body distress arising from the massive impact of biotic and abiotic stressors under conditions of anthropogenic overload. The wide distribution of mycoplasmas in nature testifies in favor of the fact that in evolutionary terms they are very successful microorganisms. In addition, mycoplasmas evolve relatively quickly. It is possible that the processes of speciation in mycoplasmas can occur in very short time intervals, which are not customary for understanding the evolutionary rates of variability and speciation. It is assumed that the evolution of mycoplasmas is oriented towards endosymbiosis. Indirect evidence of this can be found in the system by the fact that mycoplasmas specifically induce genomic rearrangements in the short arm of the 6th human chromosome.
Due to the high rate of their own evolution, mycoplasmas can be an important factor in the evolution of the biosphere. The persistence of mycoplasmas can lead to noticeable shifts in the genetic structure of a population of organisms, since genetically mediated susceptibility and sensitivity to mycoplasmal infections turn into serious pathologies of the body and, as a rule, disrupt its reproductive functions.
List of sources used
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