Restriction fragment length polymorphisms (RFLP) of cholera toxin genes in Vibrio cholerae O139 recovered from patients in Thailand, India and Bangladesh.

Since its first appearance in 1992, Vibrio cholerae O139 has caused large epidemics of a cholera-like disease in India and Bangladesh and has subsequently spread to several neighboring countries. We characterized and compared 56 V. cholerae O139 isolates recovered from patients in Thailand, India and Bangladesh by analyzing restriction fragment length polymorphisms (RFLP) of their ctx genes. The strains comprised 9 different BglI cleavage patterns of ctx genes (CT genotypes) and contained 1-4 gene copies. A total of 6 different CT genotypes were found among the 52 Thai isolates studied whereas the 2 Indian isolates and 1 isolate from Bangladesh all showed unique CT genotypes. The molecular analysis of ctx genes appeared superior to ribotyping for subspecies differentiation of O139 strains since ribotyping revealed 3 different BgII ribotypes. In addition, no correlation was found between the two methods. The molecular analysis of virulence determinants such as ctx genes in combination with other molecular techniques appears to be promising for the study of genetic changes within V. cholerae O139.