Abstract

Toxigenic strains of Vibrio cholerae belonging to the O1 and O139 serogroups cause cholera, a severe diarrhoeal disease that occurs frequently as epidemics in many developing countries. Although V. cholerae is known to be a human pathogen, the bacteria constitute part of the normal aquatic flora in the ecosystem, which includes both epidemic and non epidemic strains that vary in their virulence gene profile. V. cholerae O1 and O139 strains are commonly known to carry a set of virulence genes necessary for pathogenesis in human. The major virulence factors of V. cholerae include cholera toxin (CT), which is responsible for the profuse watery diarrhoea and a pilus colonization factor known as toxin coregulated pilus (TCP). The presence of virulence-associated genes in the environmental strains provides interesting possibility to understand the pathogenicity of the disease. The emergence of toxigenic V. cholerae strains has provided an opportunity to study the coevolution of different serogroups of epidemicV. cholerae strains, apparently driven by competition for survival and thereby attaining enhanced fitness. This review attempts to bring together some of the important researches in recent times that have contributed towards understanding the genetic, epidemiology and evolution of toxigenic V. cholerae.

Key words: Vibrio cholerae O1 and O139, wastewater, virulence-associated factors, environmental strains, mediating gene transfer.