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.