Uncommon properties of pLD105 conjugative plasmid.

Plasmid pLD105 isolated from a clinical strain of E. coli determines nitrofuran resistance due to inactivation of low-molecular-weight nitrofuran reductase subunit. pLD105 plasmid belongs to IncF. It is a conjugative plasmid and mobilizes chromosome markers, but is not transmitted to strains containing other plasmids. However, the presence of pLD105 plasmid in the recipient strain does not prevent incorporation of other plasmids, including nonconjugative ones. Transfer of nonconjugative plasmids from the donor to a recipient strain carrying pLD105 was denoted as "reverse donation".

[Pathogenicity of Francisella].

The data of literature and the results of the author's research on the pathogenicity of the causative agent of tularemia and other Francisella organisms are reviewed. The solution of the problem of their pathogenicity is based, as stated by the author, on the level of our knowledge of the genetics of Francisella. The conclusion has been made that scientific achievements in the field of the genetics of Francisella, obtained during the last 15 years, make it possible to find out the pathogenicity factors of the causative agent of tularemia, as well as other microbes of the family Francisella.

[Molecular biological mechanisms of the variability of Helicobacter pylori]. / Molekuliarno-biologicheskie osnovy izmenchivosti Helicobacter pylori.

Nowadays notions on the variability of Helicobacter pylori are reviewed. Genetic polymorphism of H. pylori is manifested by variability of gene properties and their order in different strains due to recombinations occurring in these bacteria much more frequently than in other bacterial species. H. pylori belongs to those bacteria which are capable of natural transformation. Transformation is very often observed both in vitro and in vivo. A significant role in the variability of H. pylori is played by transposons and specific nature of mutagenesis. The author emphasizes that differentiation between the roles played by recombinations and mutations in the variability of H. pylori is difficult. Special attention is paid to the resistance of H. pylori strains to chemotherapeutic drugs and to the mechanisms of its development.

[Helicobacter pylori and its role in pathology]. / Helicobacter pylori i ego rol' v patologii.

The review deals with modern data on the main cultural and biochemical properties, pathogenicity factors and their possible role in pathogenesis. Information on the methods of the diagnostics of diseases associated with H. pylori is given. The routes of the transmission of this infective agent are discussed. The results of experimental data on the genetics and immunochemistry of H. pylori are presented.

[Is not plague a "protonosis"? (the role of Protozoa in the epizootiology of plague)]. / Ne iavliaetsia li chuma "protonozom"? (o roli Protozoa v épizootologii chumy).

The author expounds the idea that soil protozoa, whose vegetative forms and cysts can harbor the plague agent for fairly prolonged periods of time, can be a major player in the epizootiology of plague. It is also postulated that the symbiotic protozoa of the digestive tract of rodents and lagomorpha can also be a reservoir of the plague agent. If this is so, among apparent epizootic cycles in mammalians in wild plague foci one should look for Yersinia pestis in the protozoa from the burrows of their primary and secondary carriers. Because parasitism of bacteria in one-celled animals is essentially epizootic, plague epizootics are presumed to be a permanent process.

[The interrelations of mucosal epithelial cells with microbes--intracellular parasites]. / O zaimotnosheniia épitelial'nykh kletok slizistykh obolochek s mikrobami--vnutrikletochnymi parazitami.

On the basis of information at hand, it can be concluded that there are principal limits on the capture of bacteria by epithelial cells in the gastrointestinal tract and other cavities. Although entry is, however, a result both of bacteria and epithelial cells, it is frequently induced by parasite-directed endocytosis and may also accompanied by passive entry of nonpathogenic bacteria. The induction of parasite-induced endocytosis should be regarded as a consequence of a fundamental concept in biology, namely: molecular and cellular recognition wherein bacterial adhesion to the host's cell receptors is of great importance. In this connection, discussion covers the origin of corresponding receptors. The authors share the opinion in that epithelial cells, those of the gastrointestinal tract in particular, are part of the human common mucosal immune system.

[Biochemical bases for the effect of combining kanamycin and nitrofuran resistance genes in Escherichia coli cells]. / Biokhimicheskie osnovy éffekta sovmeshcheniia genov ustoichivosti k kanamitsinu i nitrofuranam v kletkakh Escherichia coli.

The fact of a significant increase in resistance to aminoglycosides when nfr genes with chromosomal or plasmid localization are combined with the plasmid genes coding for kanamycin-transferase in E. coli cells is confirmed. Gel-filtration of homogenates of the cells with and without pLD105 plasmid carrying nfr gene and of the cells with a chromosomal nfr gene revealed a 10 kD polypeptide when the plasmid is present. Relying on these results, it is concluded that the discovered polypeptide fulfils two roles: inhibiting of specific nitrofuran-reductase, which leads to nitrofurans resistance and a drop of transmembrane electric potential contributing to the increase of resistance to aminoglycosides (kanamycin) in strains with the plasmid nfr gene. Absence of the 10 kD polypeptide in the cells with a chromosomal nfr gene and other data are indicative of a possible existence of a different mechanism of resistance to nitrofurans and an increase of resistance to aminoglycosides in the strains with a chromosomal nfr mutation.

[A new R-plasmid from Yersinia pseudotuberculosis]. / Novaia R-plazmida Yersinia pseudotuberculosis]

Yersinia pseudotuberculosis strain 140-P isolated from soil in the Far East was found to harbour an R-plasmid different from the plasmids that had been isolated from the bacteria previously. A new R-plasmid pLD140 is conjugation proficient and codes for the cellular resistance to streptomycin, tetracycline and sulfonamides. The plasid belongs to incompatibility group IncP. Its restriction endonucleases BamHI and SalI profile is different from the ones of the plasmids belonging to the RP4 family.

[Behavior of Sa plasmid in tularemia pathogen cells]. / Povedenie plazmidy Sa v kletkakh tuliaremiinogo mikroba.

The genome of Sa plasmid is shown to be a subject of genetical rearrangements in Francisella tularensis cells. The rearrangements either result in plasmid integration into the host cell genome or intramolecular amplification of cat-gene with the subsequent excision and recombination of the derivative plasmids. Stable inheritance of the plasmid is registered after integration while plasmid elimination occurs in case of extrachromosomal localisation.

[Study of CAT gene expression in Sa and pC194 plasmids in Escherichia coli, Francisella tularensis, and Bacillus subtilis cells]. / Issledovanie ékspressii CAT-genov plazmid Sa i pC194 v kletkakh Escherichia coli, Francisella tularensis i Bacillus subtilis.

The unit activities were defined for chloramphenicol-acetyltransferases coded for by the cat-genes of the plasmids Sa and pC194 in Francisella tularensis, Escherichia coli and Bacillus subtilis cells. Francisella tularensis cells were shown to hold intermediate position between Escherichia coli and Bacillus subtilis cells in their ability to express the genes of the different taxonomic origin. The direct dependence was found between the dose of the gene coding for chloramphenicol-acetyltransferase synthesis and efficiency of the gene expression, minimal inhibiting concentration of the antibiotic and colony size on the media containing chloramphenicol.

[Transfer of bacteriophage PRD1 genes into modified plasmid Sa of Escherichia coli and Francisella tularensis cells]. / Perenos genov bakteriofagov PRD1 v modifitsirovannye plazmidoi Sa kletki Escherichia coli i Francisella tularensis.

The donor specific bacteriophage PRDI has been shown to mediate the genes transfer into Escherichia coli and Francisella tularensis cell under certain conditions. It is necessary for the process that the recipient cells inherit the plasmids determining absorbtion of bacteriophages on the cellular surface while the transferred genes are able to be expressed. The frequencies of the tet-gene transfer from the plasmid pSKFT5 into Escherichia coli and Francisella tularensis 15 cells inheriting the plasmid Sa are, correspondingly, 10(-6) and 10(-7) clones per bacteriophage plaque.

[Features of the interaction of Escherichia coli and Francisella tularensis RNA polymerases with hybrid plasmids bearing fragments of Francisella tularensis chromosomal DNA]. / Osobennosti vzaimodeistviia RNK-polimeraz Escherichia coli i Francisella tularensis s gibridnymi plazmidami, nesushchimi fragmenty khromosomnoi DNK Francisella tularensis.

Hybrid plasmids containing the fragments of Francisella tularensis chromosomal DNA and capable of tet-gene expression both in Escherichia coli and Francisella tularensis cells were constructed. The regions of francisella chromosomal DNA binding the RNA-polymerases of Escherichia coli and Francisella tularensis were found by the electron microscopy technique. Interconnection of those regions with the expression of tet-gene of the hybrid plasmids was demonstrated.

[Comparison of the structural-functional properties of DNA-dependent RNA polymerase of the tularemia microbe and intestinal bacterial]. / Sravnenie strukturno-funktsional'nykh svoistv DNK-zaviskmykh RNA- polymeraz tuliaremiinogo mikroba i kishechnoi palochki.

The subunit compositions of RNA-polymerases from Escherichia coli and Francisella tularensis were compared. The activities of the enzymes on the corresponding chromosomal DNAs and their mixtures were defined.

[What are toxins to microbes? (the role of toxins in bacterial ecology)]. / Zachem mikrobam toskiny? (o roli toksinov v ékologii bakterii).

The author attempts to answer two questions: whether the toxins, in particular the toxins having their specificity connected with enzymatic activity, are needed for microbial cell physiology and their significance for bacteria that are not the obligate parasites for warm blooded animals. The analysis of literary data supposes the toxins to be essential cellular metabolites since many of them participate in energy acquiring. Besides that a number of toxins is shown to be relevant to microbial life and to affect the micropredators, especially the monocellular organisms feeding the microbes. In connection with the above mentioned, special attention is paid to extrachromosomal location of many toxins genes relating them to bacteriocins. The possibility is not excluded that in the future the new toxins might come to be found having the enzymatic activities.

[Fermentation of inositol by bacteria of the genus Salmonella]. / Fermentatsiia inozita bakteriiami roda Salmonella.

The capacity for the fermentation of inositol varies in different Salmonella strains. At the same time this capacity forms the basis for the determination of biovars (e. g., in S. typhimurium) and sometimes serves as the only sign for distinguishing different Salmonella sero- and biovars (e. g., S. mission and S. isangi, etc.). The study of the capacity of wild Salmonella strains for the fermentation of inositol has revealed that the fermentation of inositol is controlled by chromosomal and, seemingly, plasmid genes. In the latter case the possibility of using this sign for the biochemical and epidemiological typing of Salmonella strains is questionable.