Seasonal Variation and Molecular Characterization of Vibrio parahaemolyticus Isolated from Karnaphuni River and Estuary of Chittagong, Bangladesh

To determine whether the environmental variables governing the dynamics of Vibrio parahaemolyticus populations, sediment samples were collected with or without 1% NaCl from the Karnaphuli River and Karnaphuli Estuary of Chittagong, Bangladesh. The MPN method was used for quantitative analysis of the organisms. The isolates were subjected to biochemical tests for confirmation and also for the molecular characterization including assessment of virulence properties. Higher occurrence of V. parahaemolyticus was observed during periods of lower salinity. Thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH) are considered as major virulence factors for the organism and are coded by the tdh and trh genes, respectively. This study was, therefore, carried out to observe the seasonal variation and to investigate the occurrence of tdh and trh containing V. parahaemolyticus, besides the brackish environments. Twelve isolates out of 15 showed identical patterns to biochemical test profiles of the reference strain. This was further confirmed by PCR using primers specific for toxR gene. Antibiogram using nine commercial antibiotics showed that these isolates were sensitive to all representative antibiotics except ampicillin and streptomycin. All V. parahaemolyticus isolates were found negative for tdh gene which was confirmed by both reverse passive latex agglutination test and PCR. The most important finding of the study was the regular occurrence of V. parahaemolyticus in river of 0% salinity, though most of them are nonpathogenic strains. However, they could not grow in nutrient agar media having no NaCl.