[Emergence of toxigenic Vibrio cholerae strains on non-O1 serotype as a result of the exchange of genetic information]. / Vozniknovenie toksigennykh shtammov Vibrio cholerae ne-O1 serogruppy v rezul'tate obmena geneticheskoi informatsiei.

To study the possibilities of genetic exchange between Vibrio cholerae of O1 and non-O1 serogroups, donor and recipient strains were developed. It was shown that toxicogenic strains of V. cholerae non-O1 appeared in vitro and in vivo as the result of conjugative transfer of rfb-NAG genes from avirulent V. cholerae non-O1 strains to toxicogenic strains belonging to V. cholerae O1 classical and eltor biovars. These genes are responsible for synthesis of O antigen of non-O1 serotype. It was established that foreign rfb-NAG genes have no effect on virulence properties of a causative agent of cholera. Apparently, pathogenic V. cholerae non-O1 strains with cholera toxin genes are generated due to transfer of rfb-NAG genes under natural conditions.

[Creating a system of conjugated chromosome transfer and genetic mapping of Vibrio cholerae serogroup O139 chromosomes]. / Sozdanie sistemy kon''iugatsionnogo perenosa khromosomy i geneticheskoekartirovanie khromosomy Vibrio cholerae serogruppy O139.

A conjugational gene transfer system consisting of donor and recipient strains has been developed for genetic analysis of Vibrio cholerae 0139 serogroup, a new cholera agent. Donor strains constructed using the Tn5-Mob carrying the origin of transfer (ori T) of plasmid RP4 and helper plasmid pRP4-4 were able to perform a directed transfer of chromosomal markers. Recipient strains carried mutations in auxotrophic genes as well as in virulence genes. Based on this gene transfer system, a genetic map of V. cholerae chromosome has been created showing the order of 17 gene markers. Relationship between the genetic structure of V. cholerae 0139 and 01 is discussed.

Construction and characterization of recombinant Vibrio cholerae strains carrying heterologous genes encoding non-01 antigen or cholera enterotoxin.

In an attempt to study the effect of heterologous genes on the virulence of Vibrio cholerae 01 and non-01, rfb genes encoding biosynthesis of non-01 antigens were introduced by homologous recombination into the chromosome of V. cholerae 01 strain 569B (serotype Inaba, biotype classical). Recombinant strains were obtained which were not agglutinated with the diagnostic cholera 01 antiserum and were not sensitive to the cholera diagnostic bacteriophage, but produced as much cholera toxin as 569B and were highly virulent in the infant rabbit intraintestinal injection model. These data indicate that the rfb genes from the studied V. cholerae non-01 did not alter the virulence phenotype of V. cholerae 01. In contrast, cloned ctxAB genes from V. cholerae 01 encoding cholera toxin introduced into a non-pathogenic strain lead to efficient secretion of cholera toxin but to only low virulence in the infant rabbit model.