Studies on pathogenic Vibrio parahaemolyticus during a warm weather season in the Seto Inland Sea, Japan

Vibrio parahaemolyticus is a potentially pathogenic bacterium, occurring naturally in estuarine and marine environments throughout the world. The incidence of this organism in an aquatic environment depends upon many ecofactors. Sea water and organic material were collected during the warm weather season from a coast of the Seto Inland Sea, Japan, and analysed to determine V. parahaemolyticus densities and the occurrence of pathogenic strains, defined as those possessing tdh and/or trh genes by polymerase chain reaction (PCR), using isolated DNA from enrichment culture of the samples. About 99% of samples were positive for V. parahaemolyticus with densities of 3 to> 1400 cells per 100 ml of water or 10 g of organic samples by the most-probable-number (MPN)-PCR technique, but only 76.6% were positive by the conventional MPN culture technique, with densities ranging from 3 to> 1400 cells per 100 ml of water or 10 g of organics. Furthermore, the tdh and trh genes were positive in 41.5% and 8.5% of samples, respectively, by the MPN-PCR technique. No tdh and trh gene-positive strains were isolated by the conventional MPN culture procedure. The difference in detection between the MPN culture and the MPN-PCR techniques appeared to be significant and may be attributed to different detection sensitivities and other factors.