Populations of Vibrio parahaemolyticus in retail oysters from Florida using two methods

Vibrio parahaemolyticus is a naturally occurring estuarine bacterium that i s often associated with gastroenteritis in humans following consumption of raw molluscan shellfish. A number of studies have investigated the environm ental distribution of V: parahaemolyticus, but little is known about the le vels of this organism during distribution of oysters or at the point of con sumption. Duplicate samples of shellstock oysters were collected monthly (S eptember 1997 to May 1998) from the same four restaurants and three wholesa le seafood markets in the Gainesville, Fla. area and analyzed for total V. parahaemolyticus densities using two methods: a standard MPN method (BAM-MP N) and a new direct plating procedure (direct-VPAP). Both methods employed an alkaline phosphatase-labeled DNA probe (VPAP) targeting the species-spec ific thermolabile hemolysin (tlh) gene to confirm suspect colonies as V. pa rahaemolyticus. The highest monthly geometric mean V, parahaemolyticus dens ity was observed in October of 1997 (similar to3,000/g) with similarly high values during September and November of 1997. From December 1997 to May 19 98 mean densities were generally less than 100/g, falling to similar to 10/ g in February and March. A strong correlation (r = 0.78) between the direct -VPAP and BAM-MPN methods for determining V. parahaemolyticus densities in market-level oysters was observed. The direct-VPAP method was more rapid an d precise while the BAM-MPN was more sensitive and may better recover stres sed cells. The utilization of the VPAP probe for identification of V. parah aemolyticus sharply reduced the labor for either method compared to biochem ical identification techniques used in earlier V. parahaemolyticus surveys.