Genetic characterization of toxigenic Vibrio cholerae non-O1/non-O139 strains, isolated in the Middle Asia

Here, we report on the characterization of 22 clinical toxigenic V. cholerae non-O1/non-O139 strains isolated in the Middle Asia (Uzbekistan) in 1971–1990. PCR analysis has revealed that these strains contain the main virulence genes such as ctxA, zot, ace (CTXφ); rstC (RS1φ); tcpA, toxT, aldA (pathogenicity island VPI), but they lack both pandemic islands VSP-I and VSP-II specific to epidemic strains of O1 serogroup of El Tor biotype and O139 serogroup. Only two of the twenty two toxigenic strains have tcpA gene of El Tor type, one strain has tcpA gene of classical type, while nineteen other strains carry a new variant of this gene, designated as tcpA ^uzb. Nucleotide sequences analysis of virulence genes in toxigenic V. cholerae non-O1/non-O139 strains from Uzbekistan showed that they differ significantly from the sequences of these genes in epidemic O1 and O139 strain indicating that they belong to a separate line of evolution of virulent V. cholerae strains. For the first time it is shown that V. cholerae non-O1/non-O139 toxigenic strains of different serogroups may belong to the same clone.