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.

[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.

[Helicobacter pylori and its role in pathology].

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.

[Molecular biological mechanisms of the variability of 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.

[Is not plague a "protonosis"? (the role of Protozoa in the epizootiology of plague)].

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.

[The interrelations of mucosal epithelial cells with microbes--intracellular parasites].

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.

[Biochemical bases for the effect of combining kanamycin and nitrofuran resistance genes in Escherichia coli cells].

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.

[A new R-plasmid from 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.

[Transfer of bacteriophage PRD1 genes into modified plasmid Sa of Escherichia coli and Francisella tularensis cells].

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.

[Study of CAT gene expression in Sa and pC194 plasmids in Escherichia coli, Francisella tularensis, and Bacillus subtilis cells].

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.

[Behavior of Sa plasmid in tularemia pathogen cells].

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.

[Features of the interaction of Escherichia coli and Francisella tularensis RNA polymerases with hybrid plasmids bearing fragments of Francisella tularensis chromosomal DNA].

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].

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)].

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.

[Fermentation of inositol by bacteria of the genus 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.

[The "side-effects" of plasmids (R-plasmids and virulence)].

Many plasmids affect the host cells. Their effects cannot be explained only by the expression of the well-known genes coding for antibioticresistance, bacteriocinogeny and hemolysis or the analogous genes (side-effects). The side effects are not characteristic of all plasmids operating under similar conditions.

[Detailed mapping of the Hly-region of the plasmid pHly241. Homology of the hemolysis determinants of plasmids pHly241 and pHly195].

Data on the hemolysin synthesis determined by the plasmid pHly241, belonging to the incompatibility group I2, and its derivatives are presented in this paper. The restriction analysis of the pHly241 plasmid has resulted in the detailed mapping of the hly determinant region in the plasmid. The substantial homology has been demonstrated between the regions of the plasmids pHly241 and pHly195 coding for hemolysin synthesis and excretion from the bacterial cell.

[Transposon-mediated integration of the RP1 plasmid into chromosomes of methylotrophic bacteria].

The homology region between the DNA of plasmid RP1ts::Tn601 and chromosome of the thermotolerant methylotrophic bacterium Methylobacterium sp. SKF240 has been constructed by transposon Tn601 translocation into the chromosome. The clones of Methylobacterium sp.

[New R-plasmids in strains of Serratia marcescens with multiple drug resistance].

In 4 S. marcescens polyresistant strains isolated from patients conjugative plasmids transferred to Escherichia coli have been detected. Two of these strains carry each one plasmid which codes resistance to 10 different antibiotics, including aminoglycosides which rarely occur in our country, and belongs to group IncC.

[The role of surface structures of recipient cells in bacterial conjugation].

Previously, while studying conjugation process in bacteria, the main attention was given to donors of plasmids. The aim of this review is to show that recipient cells indeed play an important role in this process too. The main attention is given to the structure of recipient cell walls, which is necessary for the recognition of donor cell pili and the establishment of the contact between the cells, i.