Multilocus variable-number tandem repeat analysis of Vibrio cholerae O1 El Tor strains harbouring classical toxin B

Atypical Vibrio cholerae O1 strains hybrid strains (strains that cannot be classified either as El Tor or classical biotype) and altered strains (El Tor biotype strains that produce classical cholera toxin) are currently prevalent in Asia and Africa. A total of 74 hybrid and altered strains that harboured classical cholera toxin were investigated by multilocus variable-number tandem repeat analysis (MLVA). The results showed that the hybrid/altered strains could be categorized into three groups and that they were distant from the El Tor strain responsible for the seventh cholera pandemic. Hybrid/altered strains with a tandem repeat of the classical CTX prophage on the small chromosome were divided into two MLVA groups (group I: Mozambique/Bangladesh group; group III: Vietnam group), and altered strains with the RS1-CTX prophage containing the El Tor type rstR and classical ctxB on the large chromosome were placed in two MLVA groups (group II: India/Bangladesh group; group III: India/Vietnam group).