[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 CTXφ–RS1φ +VPI+VSP+/CTXφ–RS1φ–VPI+VSP+ isolates and the CTXφ–RS1φ–VPI+VSP– isolates, differing in their epidemiological significance. In the course of model experiments, it is established that nontoxigenic potentially epidemic CTXφ–RS1φ +VPI+VSP+/CTXφ–RS1φ–VPI+VSP+ isolates are derivatives of toxigenic strains.