Molecular epidemiological studies of Vibrio cholerae in Bengal region.

Vibrio cholerae isolates from environmental and clinical origins in the Bengal region in which epidemics of cholera break out periodically were analyzed with particular emphasis on the molecular epidemiological features. The presence of the virulence genes (ctxA, tcpA and toxR) in the isolates was analyzed by the PCR (polymerase chain reaction) method. PFGE (pulsed-field gel electrophoresis) was performed to determine the clonal relationships between the clinical and environmental strains. Antibiograms and O serovars of the isolates were also examined. O1 and O139 strains from both clinical and environmental sources were all positive for the three virulence genes while non-O1/non-O139 strains from both sources were all negative for ctxA and tcpA but positive for toxR. PFGE patterns of recent isolates of O1 and O139 were similar in each serovar regardless of origin, suggesting a clonal relationship between the clinical and environmental strains, although comparison with past isolates or isolates from different geographical area showed some differences.