Study of the occurrence of Vibrio vulnificus in oysters in India by polymerase chain reaction (PCR) and heterogeneity among V. vulnificus by randomly amplified polymorphic DNA PCR and gyrB sequence analysis.

The pathogenic bacterium Vibrio vulnificus is widely distributed in estuarine waters throughout the world. In this study, the presence of V. vulnificus in oysters was studied both by conventional culture and DNA-based molecular technique. Following enrichment in alkaline peptone water (APW), the bacteria were lysed and a nested polymerase chain reaction (PCR) for vvhA gene was performed. The effect of duration of enrichment on the sensitivity of detection by PCR was evaluated. The organism was isolated from 43% of samples after 18 h enrichment in APW by conventional culture method. Nested PCR amplifying a fragment of vvhA gene detected the organism in 11%, 60% and 81% of samples following 0, 6 and 18 h of enrichment. All the biochemically identified V. vulnificus strains possessed vvhA gene and belonged to biotype 1. The genetic relatedness among the strains was studied by randomly amplified polymorphic DNA (RAPD) PCR and gyrB sequence analysis. The results suggest the presence of two distinct clonal groups of V. vulnificus in oysters in India. The study demonstrates, for the first time that gyrB sequence analysis could be used to study the genetic diversity of V. vulnificus.