MOLECULAR-GENETIC PROPERTIES OF VIBRIO CHOLERAE EL TOR STRAINS CIRCULATING IN AFRICA.

The review contains some brief information on cholera epidemics in Africa. Based on the results of the whole genome sequencing of 30 clinical strains isolated in Africa in different periods of the 7th cholera pandemic (1985-2012), extensive genetic diversity has been revealed. It is demonstrated that at present cholera epidemics in Africa are caused by new variants of the agent, which emerged in South- Eastern Asia in consequence of not only new genes acquisition, but also genome alterations of pandemicity and pathogenicity islands. SNP analysis of 53 strains circulating at different times in the territory of the continent, as well as isolated in South-Eastern Asia, has been carried out. Phylogenetic relations between the majority of the African and Asian strains have been established. In addition, strains were shown to exist that are, apparently, endemic to the African region. Identified genetic diversity of the strains with varying virulence and drug resistance points out the necessity of continuous molecular monitoring of the cholera agent in Africa.

STRUCTURAL ORGANIZATION OF PORIN GENES (INTACT AND DISRUPTED BY IS 100) BORDERING THE PGM LOCUS OF THE YERSINIA PESTIS AND YERSINIA PSEUDOTUBERCULOSIS STRAINS.

In highly virulent strains of Yersinia pestis, the porin gene border- ing pigmentation (pgm) locus was observed to be usually broken by IS100. In this case, the pgm locus that carries virulence genes (high pathogenicity island) and biofilm formation genes (hms operon) is flanked by direct copies of IS100, which can cause its destabilization. We studied the prevalence of the intact and dis- rupted porin genes among 240 strains of Y. pestis from 39 natural centers in Russia and abroad, and 68 strains of Yersinia pseudotuberculosis from different geographical regions. The majority of the highly virulent Y. pestis strains and some phylogenetic lines of Y. pseudotuberculosis 0:1 serotype contain disrupted porin genes. At the same time, deletion of the pgm locus by flanking IS100 in Y pseudotuberculosis is impossible, because IS100 is integrated in the porin gene in the reverse orientation as compared to Y pestis. The porin genes are intact in all Y pestis strains with low epidemic importance and some phylogenetic lines of highly virulent Y pestis strains from some desert foci and Caspian sandy focus, as well as most strains of Y pseudotuberculosis 0:1 serotype. Less virulent strains of Y pseudotuberculosis 0:3 serotype revealed extensive deletion, which included the porin gene and a portion of the gene astE. The nucleotide sequence of the porin genes in Y pestis and Y pseudotuberculosis strains from different geographical regions are identical. Three alleles of the porin gene differ solely by the site of integration and orientation of IS 100 or by the lack of integration. The nucleotide sequence of IS 100, embedded in the porin gene of Yersinia, has minor differences only in two Y pestis strains isolated in America. Low frequency of Hms- mutations correlates with the intact condition of the porin gene in Y pestis. This correlation is absent in Y pseudotuberculosis.

[Genome structure and origin of nontoxigenic strains of Vibrio cholerae of El Tor biovar with different epidemiological significance].

Intraspecies genetic differentiation of nontoxigenic strains of Vibrio cholerae of El Tor biovar containing one of the key pathogenicity genes, tcpA, is studied along with the phylogenetic relationships between these strains and toxigenic isolates. Comparative analysis of the whole genome nucleotide sequences demonstrates for the first time that ctxA ­ tcpA + strains vary considerably and can be clustered into two separate groups, the CTXφ­RS1φ +VPI+VSP+/CTXφ­RS1φ­VPI+VSP+ isolates and the CTXφ­RS1φ­VPI+VSP­ isolates, differing in their epidemiological significance. In the course of model experiments, it is established that nontoxigenic potentially epidemic CTXφ­RS1φ +VPI+VSP+/CTXφ­RS1φ­VPI+VSP+ isolates are derivatives of toxigenic strains. The results of whole genome SNP analysis of 35 Vibrio cholerae strains confirm these data and indicate genetic remoteness of nontoxigenic CTXφ­RS1φ­VPI+VSP­ strains both from the potentially epidemic strains and from the toxigenic isolates. It is found that the genomes of the CTXφ­RS1φ­VPI+VSP­ strains contain unique SNPs which are characteristic of them alone. The new data on the structure of the genome of nontoxigenic strains with different epidemiological significance may be further used for their genetic differentiation.