Distribution and sequence analysis of virulence associated genes in Vibrio cholerae O1, O139 and non-O1/non-O139 isolates from Thailand.

Virulence-associated genes of Vibrio cholerae including O1, O139 and non-O1/non-O139 from an outbreak in Songkhla Province and sporadic cases occurred in Thailand during 1993 - 2002 were investigated. One hundred eighty-five V. cholerae strains were examined for the presence of virulence-associated genes including ctxA, tcpA, zot, toxR, toxS, toxT, and ace by polymerase chain reaction. DNA sequences of ctxA, tcpA, zot and toxR also were investigated in 8 selected isolates. Results showed that the virulence factors genes were distributed in the majority of V cholerae O1 biotype Inaba and Ogawa strains (85-97%). All 6 strains of the O139 harbored toxR, toxS and toxT whereas ctxA, tcpA, zot and ace were detected only 50-67%. Toxins genes found in non-O1/non-O139 strains ranged 8-30% except toxR (73.5%). Results of multiple sequence alignments among the isolates compared with V. cholerae O1 in database (embl M21249), showed that ctxA, tcpA and zot sequences in all 8 isolates were conserved, but base changes were found in toxR sequence. These molecular characteristics of V cholerae isolated from Thailand will provide detailed information for facilitating future studies on the development and design of appropriate vaccine providing protection against local strains.