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The analysis of opportunistic bacteria phenotypic and genetic virulence markers indicates that pathogenicity formation is based on a structural modification of bacterial DNA which is linked with migration of interbacterial pathogenicity "islands" genetic determinants. Structural organization features of these mobile genetic elements determine high expression probability, and PCR detection of pathogenicity "islands" determinants that control adhesins, invasins, cytotoxic and cytolitic toxines synthesis may indicate etiopathogenetic significance of clinical isolates.

The detection by PCR of virulence markers in clinical strains of Escherichia coli strains producing the shiga-like toxin.Thirty-four strains of STEC isolated from patients with acute intestinal infection were studied. PCR with primers to following 10 genes of pathogenicity: rfbE, eaeA, iha, saa, stx1, stx2, cdt, cubA, ehx and espP was utilized. Susceptibility of isolated to antibiotics was determined. Presence of class I integrons in bacterial cells was assessed.rfbE gene coding antigen of serogroup O157 was detected in 31 out of 34 isolates. Twenty-three (74.2%) strains of E. coli O157 had typical pattern of pathogenicity genes (rfbE, eaeA, stx1, stx2, ehx, and espP). In 12 out of 23 cultures (52.2%) sequence of iha gene was detected. Presence of cdt genes was revealed only in 2 clonical isolates belonging to serogroup O157 isolated in Moscow. Two out of 11 strains isolated in Tula region did not have rfbE and eaeA sequences but had sequences saa and subA, which were absent in other studied strains of STEC. Genes of class I integrons were not found in all studied strains although some of them were resistant to sulfonamides, tetracyclines, and aminoglycosides.Heterogeneity in pattern of pathogenicity genes was demonstrated in E. coli producing shiga-like toxin that points to circulation of different cultures among patients with acute intestinal infection, which is necessary to consider during analysis of clinical isolates.

Comparative study of 97 cultures of enterococci, including reference highly virulent strain Enterococcus faecalis ATCC 259212, 35 clinical isolates of E. faecium, 58 isolates of E. faecalis, and 3 probiotic strains of E. faecium: Linex (Lek company, Slovenia), SF68 (Bifiform, Denmark), and L3 (Avena, Russia). Thirteen of 93 cultures were isolated from patients treated with probiotic Linex, containing E. faecium (Linex) bacterium. Comparative analysis of cultures on the presence of 8 genes determining virulence (esp, asa1, efaA, cylA, cylM, gelE, sprE, and fsrB) was performed using polymerase chain reaction and testing with antibiotics. It was established that in some cases clinical cultures of enterococci used for analysis carried genes of pathogenicity and were not related to E. faecium (Linex) strain included in composition of the probiotic drug.

Current microbiological data on the vaginal microecology in healthy women and in patients with bacterial vaginosis are presented in the article. Problems of formation of colonization resistance of vaginal microbiocenosis were discussed. Etiologic role of certain microorganisms and their associations in the pathogenesis of bacterial vaginosis was considered. Pathophysiological processes leading to development of vaginal disbiosis, features of local immune status and molecular specificity of intercellular interactions in the development of adaptive immune response were characterized.

The purpose of the review is to analyze the scientific progress to date about the role of opportunistic gut bacteria in development of diseases in humans. Mechanisms of tolerance of local gut immune system to transitory normal microflora, translocation of bacteria and endotoxins in normal and pathology, possible routes of transmission of infectious agents and endotoxins which lead to systemic inflammation syndrome and affection of various organs were discussed.

The authors show perspectives of using primers detecting nucleotide gene sequences in isolated E. coli strains; pathogenic factors of E. coli, fimbrial adhesive (type I and type P); alpha-hemolysin (hly); cytotoxic necrotising factor I (cnf-1); iron-regulated proteins for predicting the course of the inflammatory process in urological patients with bacterial infection.

The human disease caused by avian influenza virus in South Asia is a typical example of emerging infection resulting from transmission of a known causative agent to a new host. The first cases with a comparatively high level of lethality rates among patients were registered in 1997 and 1999. The situation is a special phenomenon in epidemiology which requires deep evolutionary and ecological analysis, as well as theoretical interpretation. With the example of avian influenza virus in Western Europe and South Asia in 2003-2004 the practical expediency of modern concepts "foci versus epidemics" and "eradication versus vaccination" is now evident.

The relationship between the presence, or the absence, of conjugative plasmid pR50 detected in Klebsiella oxytoca 89, in the isogenic pairs of attenuated strains Shigella flexneri 2a 516 Near and Salmonella typhimurium 129 Rifr and the regeneration of the active forms of oxygen by mouse peritoneal phagocytizing cells was studied. As indicated by the data obtained in the course of the experiment, plasmids pR50 could influence the chemiluminescent response of phagocytes. The inhibition of the synthesis of oxygen metabolites was found to occur at the primary stage of the infectious process, that later this synthesis increased, that facilitated the survival of the animals infected with the cultures carrying plasmid pR50.

Data on the secreted pathogenicity factors of different enterobacterial species are reviewed. Update information on toxin classification is presented. The main cytotoxic and cytotonic enterotoxins, transient pore forming toxins (RTX), cytotoxic necrotizing factor and injection toxins have been analyzed. Problems connected with the mechanism of action and genetic control of known enterobacterial toxins are discussed.

The information on the key pathogenicity factors of uropathogenic and enteropathogenic Escherichia coli, Shigella, Salmonella, Vibrio cholerae, Yersinia, Listeria and Helicobacter pylori is reviewed. The analysis of data on pathogenicity "islands" and "islets" of infective agents is given. The problems of the genetic control of pathogenicity factors and the functions of pathogenicity "islands", found in infective agents, are discussed.

Immunosuppressive activity of Salmonella typhimurium extracellular lipopolysaccharide (LPS) was studied. In this study isogenic S. typhimurium strains with different degree of virulence were used. The attenuation of these strains was linked with mutations on their chromosome (altered synthesis of RNA polymerase or gyrase DNA) or their own virulence plasmid (the insertion of transposon Tn-5). To obtain LPS fraction with different molecular weights, the filtrate of bacterial culture was subjected to gel filtration through a column packed with Sephadex G-200. The immunosuppressive action of LPS fractions was determined on the model of delayed-type hypersensitivity to nonbacterial antigen in experiments on BALB/c mice. The study revealed that transposon-mediated mutation on plasmid, accompanied by the attenuation of salmonellae, led to the loss of immunosuppressive activity of the high-molecular heat-sensitive component of LPS; only the second heat-resistant component with medium molecular weight retained its activity. The presence of two chromosomal attenuating mutations (rifr nalr) was accompanied by the loss of immunosuppressive activity in both components of LPS.

The paper presents and analyzes the results of experiments on the Escherichia coli-Salmonella relationships in combined infection of Ornithodoros papillipes ticks. The findings have led to the following conclusions. The body of hungry adult O. papillipes ticks can retain the pathogen of Salmonella infection for a month. This model object is also favourable for avirulent E. coli strain persistent in the body's cavity both alone and in combination with Salmonella typhimurium strain in a 1:1 ratio. Binary carriage in hungry Ornithodoros papillipes ticks revealed that the ticks associated with Salmonella typhimurium and E. coli 083 mcl + lyz No 225, microcine and lysozyme producers, are freed of pathogenic bacteria during 24 hours. The initial bacteria E. coli 083 mcl also suppress salmonellae; however, their elimination occurs much later--in 5 days. Calculating the correlation between the pairs (S. typhi and E. coli) has revealed a linear functional relationship of the rate of E. coli growth to S. typhimurium suppression.

The latest data concerning the characterization of the pathogenicity factors of bacteria and the evaluation of their role in the realization of definite phases of the development of the infectious process are presented. The infectious process is regarded as the result of the complicated simultaneous interaction of microorganisms and different cells and tissues of the host body. The problems of the polydeterminant character of pathogenicity factors, tho possibility of the joint action of different factors at one and the same stage of the development of the infectious process and, vice versa, the action of the same factors at different stages of the interaction of the infective agent and the susceptible host are discussed. Modern data on the genetic control of pathogenicity factors, on the localization of their genetic determinants on the chromosome and the virulence plasmids, information of pathogenicity "islets" which jointly determine the pathogenic potential of the infective agent are given. The emphasis is made on fact that the general principle of the genetic control of bacterial pathogenicity is complicated relationship between chromosomal and nonchromosomal determinants; some of them form a part of genetic pathogenicity "islets", simultaneously regulating and expressing the pathogenicity factors of the infective agent.

In 108 K. pneumoniae clinical strains isolated in pneumonia (32 strains), inflammatory processes of the urinary tracts (36 strains) and toxicoseptic states (40 strains) caseinolytic, gelatinase, phosphatase, lecithinase activities and the capacity for producing DNAase and RNAase were studied. The presence of caseinolytic activity was found in 38 cultures (35.1%), gelatinase activity in 37 cultures (34.2%) and lecithinase activity in 13 cultures (12.0%). The production of RNAase was noted in 74 strains (68.5%), DNAase in 56 strains (51.8%) and acidic phosphatase in 33 strains (30.5%). The role of the above-mentioned enzymes in the development of purulent inflammatory processes, as well as the importance of further studies, including those aimed at establishing the nature of the genetic control of the already known properties of the pathogen, are discussed.

S. sonnei virulent strain containing invasiveness plasmid pSS120 was found to suppress delayed hypersensitivity (DH) to nonbacterial antigens. In the filtrate of the culture of this strain extracellular lipopolysaccharide (LPS), capable of inducing immunosuppressing activity in nonvirulent bacteria, was detected. S. sonnei strain having plasmid pSS120 whose invasiveness genes were blocked by the penetration of transposon Tn5, as well as strains containing no invasiveness plasmid, proved to be nonvirulent and could not inhibit immunosuppressing action. Extracellular LPS of nonvirulent strains had no inductive immunosuppressing activity. But it could be activated by chemical treatment. The results of this study indicate that the immunosuppressing action of S. sonnei LPS were linked with some genes of invasiveness plasmid pSS120.

The suppressing activity of lipopolysaccharide (LPS) of the filtrates of genetically related S. typhimurium 415 and 415/307 cultures with respect to delayed hypersensitivity to nonbacterial antigen in mice was studied. In LPS of the virulent strain two immunosuppressing fractions differing in their molecular weight were detected by the method of gel filtration. One of them was detected in LPS of the genetically related nonplasmid clone of S. typhimurium 415/307. The possibility of the chemical inactivation and reactivation of the immunosuppressing properties of LPS was shown.

In this work summarized data is presented on the molecular and biological characteristics of the representatives of the genus Shigella, the genetic determination of their pathogenicity factors contributing both to the initiation of the development of the infectious process and to the formation of pathological changes in the host body. The problems of the construction of live Shigella vaccines are considered, as well as the development of new diagnostic tests, based on the data on deciphering the structure and functions of pathogenicity factors which determine the invasive properties of Shigella.

An immunosuppressive effect produced by live microbial cells of S. flexneri virulent plasmid-carrying strain 2a 516 (pSF 140-) was shown in relation to the formation of splenic cells producing antibodies to heterologous antigen (sheep red blood cells). This effect was most pronounced at an early period (days 4-7) after the infection of mice. On the contrary, avirulent plasmid-free variant (pSF 140-), genetically related to S. flexneri strain 2a 516, produced an immunostimulating effect at this period of observation. Such immunostimulating action of S. flexneri plasmid-free variant of the smooth type on immunocompetent effector T and B lymphocytes with the preservation of active hematopoiesis is indicative of the possibility of using these variants of shigellae as vector strains in constructing gene engineering (vector) vaccines.

Fractions of S.flexneri 2a 516 outer membrane proteins determined by plasmid pSF140 have been shown to possess immunomodulating activity and to be capable of influencing the intensity of hematopoiesis, manifested by the stimulation of endocolony formation, the increase of the amount of splenic colony-forming units in the marrow, the increase of the pool of proliferating splenic colony-forming units of the marrow and their intensive migration into the blood. Outer membrane proteins have been shown to produce an immunostimulating effect on the functional activity of effector B-lymphocytes shortly after their injection. On the contrary, S.flexneri 2a 516/4 pSF140- outer membrane proteins produce a less pronounced effect on hematopoietic stem cells and reproduce unspecific immunostimulating effect on the formation of B-cells, synthesizing antibodies to heterologous antigen.

The authors analyze current data on genetic control of the principal factors of pathogenicity of Shigella, Salmonella, Yersinia, Listeria and Proteus. They review the phases in the development of an infectious process and discuss problems in interaction of chromosomal and plasmid genes determining the pathogenicity of the said bacteria.

The article deals with the data obtained as the result of the comprehensive study of K. pneumoniae antilysozyme factor, playing an essential role in the infectious pathology of weakened children and adults, as it was recently established. The study has revealed that the genes that determine the synthesis of the antilysozyme factor can be localized on the plasmid, tentatively designated pAlz60 and expressed in a wide circle of hosts of the family Enterobacteriaceae, belongs to type fi-, compatibility group Pl. Experiments with genetically related pairs of strains, differing by the presence of plasmid pAlz60, have demonstrated that factor ALz has no influence on the interaction of bacteria with the epithelium, but contributes to the suppression of phagocytosis, the preservation and multiplication of strains having this factor in the phagolysosome. Alz character has been classified with pathogenicity factors ensuring longer persistence of the infective agent in the body. The characterization of the chemical structure of the antilysozyme factor functioning as an inhibitor of lysozyme is presented. The method for the rapid determination of the antilysozyme activity of bacteria has been developed. This method may be used for the evaluation of isolated strains as regards their clinical and epidemic importance.

The interaction of Shigella recombinant strains (with attenuating chromosomal mutations, with transposon-neutralized plasmid gene mutations, the hybrids of both strains), incapable of inducing keratoconjunctivitis in guinea pigs, with cells Hep-2 and enterocytes in the ligated loop of the small intestine of rabbits was studied. These strains retained, to varying extent, pronounced adhesiveness, but practically lost their invasiveness (though in Peyer's patches the translocation of bacteria by M-cells was observed) and cytotoxicity, as well as their capacity to multiply in epithelial cells and to cause destructive inflammation in the intestine. According to these criteria of evaluation, morphological investigations confirm the safety of the recombinant shigellae under study.

In 2-3 weeks after the oral immunization of rabbits, made in one or two administrations, with attenuated two-marker S. dysenteriae 1 strain VS-12 and recombinant S. dysenteriae VS-12/S. sonnei NR-18 and S. flexneri y433/S. sonnei NR-18 pronounced immunological reaction developed in the mucous membrane of the small intestine: blast transformation follicles of Peyer's patches, an increase in the number of lymphoblasts and plasmocytes in the cupolae of follicles and in intestinal villi, and an increase in the number of lymphocytes and macrophages in the intestinal epithelium with their release into the lumen of the intestine after challenge with virulent shigellae. The protective potency of these recombinants after challenge with massive doses of virulent shigellae was found to be high, which was shown by quantitative evaluation of the decrease of adhesion, invasiveness and cytotoxicity, suppression of epithelial lesions and development of inflammation in the intestinal mucosa.

Chickens over 10 days old, infected orally with virulent salmonellae, were found to remain alive. Histologic investigation showed the development of mild enteritis and more pronounced, lasting for more than two weeks, inflammation of the cecum, dissemination and focal lesions in the liver (granulomas, necrosis). In experiments on the oral immunization of 3-day old chickens the bivalent hybrid of S. typhimurium vaccine strain 274 and S. dublin induced only pronounced blast transformation in lymphatic follicles of the cecum, hyperplasia of activated macrophages and formation of granulomas from these macrophages and lymphocytes. After oral challenge of the immunized chickens with virulent salmonellae of group B (S. typhimurium) and group D (S. enteritidis, S. gallinarum-pullorum) the chickens exhibited sharply pronounced protection against adhesion, colonization and invasion, and a few penetrating bacteria were rapidly destroyed by immune macrophages. Hybrid strain 274/O9 proved to be suitable for use as oral bivalent vaccine against salmonellosis in chickens.

A nonvirulent strain of Shigella sonnei phase I has been obtained by integration of the transposon Tn5 into the invasiveness plasmid pSS120 in the virulent strain and designated NR18. The presence of the plasmid pSS120 in both strains results in the similar morphology and bacterial ability to agglutinate in the presence of antiserum to Shigella sonnei phase I antigen. The lipopolysaccharide preparations from the virulent and nonvirulent strains give the similar reactions with the antiserum in the reaction of hemagglutination. However, in the reaction of passive local hemolysis in the gel (Jerne reaction) the significant difference is revealed in the immunogenicity of the preparations, with the preparations from the virulent strain being 4-5 fold more immunogenic. In crossreaction, the antibodies secreted by the mouse spleen cells immunized by LPS from the virulent strain show a weak reaction with the ram erythrocytes sensitized by the LPS of the nonvirulent strain. Thus, the biological changes in the LPS of the nonvirulent strains that are, evidently, the consequence of the structural changes, are identified only by the most sensitive immunological techniques.

Mutations resulting in acquisition of the resistance to rifampicin, streptomycin, neamine, polymyxin M, mecillinam and high concentrations of nalidixic acid were studied with respect to their effect on virulence of Shigella flexneri by transduction of the markers from the spontaneous avirulent mutants to the initial strain. It was shown that the acquisition of the determinants of the resistance to rifampicin, streptomycin, neamine (nea A) and high concentration of nalidixic acid resulted in 100 per cent of the cases in losing the transductant capacity for causing keratoconjunctivitis in guinea-pigs. With the mutations resulting in the acquisition of resistance to neamine (nea B) and mecillinam virulence was lost only in a part of the clones (33 and 53 per cent respectively). The changes in the pathogenic properties of the transductants with the acquired markers of the resistance to the above antibiotics were associated with impairment of the bacterial cell vital structures. It is suggested that the genetically characterized avirulen immunogenetic mutants be used as potential vaccinal strains.

The authors studied the role played by Sac-plasmide of atypical S. newport strains inducing a more severe course of the disease in the development of the infectious process in man. In experiments with genetically-bound strains of salmonellae and E. coli K12, differing by the presence of Sac-plasmide, it was shown that the acquisition or the loss of the latter failed to effect significantly the capacity of the microbes to cause death of chick embryos infected on the membrane, to reproduce in the pulmonary tissue of mice infected intranasally, and affect the cells of the L1 strain. Genetic confirmation of the absence of any connection between the sucrose sign determined by plasmide and the capacity of the strains to cause dilatation of the ligated rabbit intestinal loop was presented. The data obtained indicated that high virulence of the S. newport strains under study was not associated with the presence of Sacplasmide in them.

Sh. flexneri mutants No. 2a, resistant to phosphomycin (25 microgram/ml), differ in their fermentability in respect to glucose, mannitol, mannose and fructose. The mutants fall into 7 groups by this characteristic. All the resistant mutants, irrespective of the type of hydrocarbon fermentation, have lost their ability of causing keratoconjunctivitis. The decreased virulence of the phosphomycin-resistant mutants is linked with the loss of their penetration properties, although their adhesiveness and proliferative capacity on the surface HeLa cells is retained. A change in the virulence of the mutants under study is not connected with disturbances in the synthesis of O-antigen LPS. Most of these mutants are highly immunogenic.

The oxygen uptake and dehydrogenase activity of avirulent xyl+ and xyl- str hybrids (KCP-), obtained from virulent strains Sh. flexneri (Sh. flexneri 222 5 a and Sh. flexneri M42-432a) and donor strain E. coli AB 313, devoid of ability for intracellular multiplication in epithelial cells are studied. Some tricarboxylic acid intermediates, hexoses and pentoses were used as substrates. A definite tendency has been established, indicating a decreased rate of oxygen consumption and dehydrogenase activity of the hybrids, compared to the respiratory activity of the virulent recipient strains tsh. flexneri in all substrates used.

The electron microscopic study of cells HEp-2 and the complex microbiological and morphological study of tissues and organs of guinea pigs and mice infected with the isogenic pairs of Yersinia strains (Y. pseudotuberculosis I and Y. enterocolitica 09) differing in the presence of the calcium-dependence plasmid, as well as Y. pseudotuberculosis mutants resistant to rifampicin, nalidixic acid or crystal violet without this plasmid, have revealed that the invasiveness and cytotoxicity of the infective agents are not directly related to the presence of the above-mentioned plasmid in these bacteria. The use of the quantitative characteristics of virulence, such as penetration ability, intracellular multiplication, dissemination and the formation of degenerative changes, has made it possible to find out that the mutants of Y. pseudotuberculosis I, yielding the negative result in the keratoconjunctivitis test and resistant to the above-mentioned antimicrobial substances, can be arranged in the following order according to the degree of attenuation: rifr mutants--nalr mutants--kvlr mutants. In contrast to Y. pseudotuberculosis I, the loss of the calcium-dependence plasmid by Y. enterocolitica 09 is accompanied by an essential decrease in their invasive and cytotoxic properties, but this relationship is indirect and unstable. The proposed criteria intended for use in the evaluation of the degree of the manifestation of the invasive and cytotoxic properties of bacteria can be useful for the selection of optimally attenuated Yersinia strains showing promise as vaccine strains.

The catalase and phosphatase activity of avirulent by keratoconjunctival test of guinea pigs xyl+ and xyl-str (KCP-) hybrids that have lost their ability for intracellular multiplication, received from virulent strains. Sh. flexneri (Sh. flexneri 222 5 a and Sh. flexneri M42-43) and donor strain E. coli AB 313 was investigated. It is established that there is a definite dependence between the changes in the catalase and the phosphatase activities of the hybrid strains and the newly received by the hybridization genetic information. The enzyme activity of the hybrid strains always correlated with the level of this activity in the donor strains E. coli.

One of the aspects of antagonistic relations could be the competence of microorganisms for specific sites of attachement to the epithelium common for shigellae and some E. coli serological types; this was demonstrated on a model of shigella-induced keratoconjunctivitis and in experiments with the HEp-2 cells infected with H3-glucose-labeled Sh. flexneri 5a, with combined administration of the latter with E. coli 08 and 028. The data obtained emphasized the importance for the development of the infectious process of the primary stage of shigella attachment to the epithelium. It was also revealed that the presence of common pili in the strains or production of colicine by bacteria intensified the antagonistic activity of E. coli, irrespective of their serological type.

Epithelial cells of the HEp-2 line infected in parallel by genetically connected strains of Sh. flexneri, differing in the capacity to synthesize the type antigen were studied morphologically. The type antigen proved to show no significant influence on the penetration of dysentery bacilli into the cell. A study of the process of phagocytosis of the mentioned strains by a culture of peritoneal macrophages of guinea pig demonstrated that the presence of a type antigen communicated to the bacteria some selective advantages within the macrophages increasing their resistance to the action of the digestive enzymes.

The study of the use of scanning electron microscopy and the analysis of the initial stages of interaction between S. typhi and eukaryotic cells by the method of three-dimensional reconstruction has revealed that the infective agent penetrates into the cytoplasm on the principle of internalization. The internalization of S. typhi occurs with the active participation of the eukaryotic cells which, at the beginning, envelopes the bacteria with its processes, and the infective agents firmly adhere to the glycocalyx of the host cell by means of special fimbria-like formations differing from fimbriae by their lesser rigidity and thickness; then the microbes fixed to the membrane penetrate inside the cell without destroying its cytoplasmic membrane. Differences in the processes of the interaction of eukaryotic cells with S. typhi initial strain 238 and its variant free from the plasmid with a molecular weight of 6 Md, characterized by its lower capacity for association with cells of continuous cell culture L929, have been revealed. The factors stimulating the ingestion of S. typhi by eukaryotic cells are under study at present.

A review and analysis of data on the investigation of factors concerning the initial events of interaction of Shigella with epithelial cells: attachment of penetration are presented. In the experiments with 3H-labeled bacteria it was shown that although common pili confer adhesive properties to bacteria but the penetration of Shigella into the cell is not increased. It was stated that LPS of Shigella O antigen plays an important role not only in interaction with cellular and humoral factors of the macroorganism defence but also in an initial stage of attachment of bacteria to the membrane of epithelial cells. However LPS of O antigen does not provide the penetration of the agent into the cell. In filtrates of virulent strains of Shigella flexneri, in contrast to those of smooth mutants and hybrids, lacking penetration ability, a biologically active factor (BAF) of protein or lipoprotein nature which reduced the LD50 of virulent and avirulent bacteria in infection of chicken embryos on chorioallantoic membrane, decreases ID50 and complicates the course of the infectious process in conjunctival infection of guinea pigs with virulent Shigella strain was revealed. S. flexneri transductant with a restored ability to induce kerato-conjunctivitis restored an ability to produce the BAF as well. Comparison of these data with the findings of other investigators was carried out. Perspectives of interpretation of penetration mechanism of Shigella into epithelial cells are discussed.

Oxygen uptake and dehydrogenase activity are studied with lac+ kcpminus hybrids of Shigella flexneri, being avirulent to the eyes of guinea pigs, because of having lost ability for penetration in epithelial cells. These strains were obtained by hybridization of the virulent strain Shigella flexneri 222 5 a with the Hfr strain Escherichia coli K-12 P4x. It is established that lac+ kcp minus hybrids are characterized by significant decrease of respiratory activity. This decrease is outlined as a tendency studying O2 uptake and is extremely well expressed studying the dehydrogenase activity. The tests being performed with these hybrids show that the loss of virulence and connected with it the loss of the ability for penetration is related to a decrease of the respiratory activity of these bacteria which supply a part of the energy needed for their viability.

The authors describe an effect of suppression of invasion of the guinea pig eye conjunctiva and the HEp-2 epithelial cells by virulent Sh. flexneri bacilli, with a simultaneous administration of the same dose of avirulent shigella mutants, genetically connected with them. The data of morphological study and experiments with 3H-glucose labeled shigellae carried out on the cell species model indicated that the bacterial competition for the specific sites for absorption on the epithelial cells underlay the observed phenomenon.

The glycolysis (aerobic and in the presence of KCN) of avirulent xyl+ and xyl-str hybrids Sh. flexneri x E. coli, devoid of their ability to multiply intracellularly in the epithelial cells, is studied. It is established that their glycolytic activity is considerably higher than the activity of the donor strain E. coli, and deviate significantly compared with shown activity of the virulent recipient strains Sh. flexneri. Xyl-str hybrids are showing high values of glycolysis in aerobic conditions and in the presence of KCN, while in xyl+ hybrids very active glycolysis is observed only in the presence of KCN - probably completely sufficient for the persistence of bacteria in the host-cell at anaerobic conditions.

Complex microbiological and morphological study of the genetically connected Sh. flexneri strains, avirulent by keratoconjunctival test showed that the greatest extent of the virulent loss was revealed in shigellae with mutation in the area glpK-gene: they lost the capacity to penetrate into the cells of the bronchial epithelium, to resist local leukocytic reaction and to produce an injurious action on the pulmonary vessels. Shigellae with the replaced kcpA- gene area mostly lost the capacity to penetrate into the epithelial cells of mouse bronchi and were eliminated from the epithelium by the 9th hour after the administration. Xyl--avir-hybrids obtained from crossing of Sh flexneri with the streptomycin-resistant E. coli K12 donors were characterized by the loss of the capacity to prolonged reproduction in the organism of mice with the retention of the capacity to penetration into the epithelium, of the influence on the development of the leukocytic reaction and of the damaging effect on the pulmonary capillaries.