Comparative Analysis of Molecular-Genetic Properties in Non-Toxigenic Vibrio cholerae O1 Strains Biovar El Tor, Isolated in Russia and on Cholera Endemic Territories

Objective of the study was to perform a comparative analysis of molecular-genetic properties in non-toxigenic Vibrio cholerae O1 strains biovar El Tor, isolated in the Republic of Kalmykia and on cholera endemic territories and to reveal their phylogenetic relations to toxigenic isolates.

Materials and methods. We have carried out bio-information analysis of whole genome sequences of 60 cholera vibrio strains from endemic as regards cholera regions and from Kalmykia. The presence of pathogenicity and endemicity islands in their genomes has been determined. Specifed have been the sequence-types of the examined strains and whole genome SNP-analysis conducted.

Results and discussion. Non-toxigenic El Tor vibrios circulating in Kalmykia are clustered into two major genotypes: ctxA^–tcpA⁺VPI-2⁺VSP^– and ctxA^–tcpA^–VPI-2Δ⁺VSP^–, where VPI-2 Δ⁺ signifes the presence of deletions of varying length in the genome of this pathogenicity island. Only the latter one is found in regions endemic for cholera. In addition, ctxA^– tcpA⁺VPI-2⁺VSP⁺ populations circulate in cholera endemic foci, not found in Kalmykia. 17 sequence-types were identifed among the studied strains (by seven housekeeping gene loci). Phylogenetic analysis performed using SNP-typing demonstrated the absence of close genetic relation between the ctxA^–tcpA⁺VPI-2⁺VSP^– vibrios from Kalmykia and both toxigenic and non-toxigenic vibrios with different composition of pathogenicity and pandemicity islands in the genome. At the same time, genetic proximity of ctxA^–tcpA^–VPI-2Δ⁺VSP^– cholera vibrios from endemic cholera foci with those isolated in Kalmykia was detected, which may indicate the possibility of their recurrent importation into the territory of Russia. Non-toxigenic V. cholerae strains found in the territory of Kalmykia are characterized by a high genetic diversity. Circulation of the strains with unique sequence-types suggests their potential for long-term persistence on this territory. At the same time, phylogenetic closeness and identity of certain strains with strains from endemic territories can be an evidence of repeated importation.

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