Scientific Publications by FDA Staff

Appl Environ Microbiol 2016 Jul 15;82(15):4517-22

Effects of intertidal harvest practices on Vibrio parahaemolyticus and Vibrio vulnificus levels in oysters.

Jones JL, Kinsey TP, Johnson LW, Porso R, Friedman B, Curtis M, Wesighan P, Schuster R, Bowers JC

Vibrio parahaemolyticus and Vibrio vulnificus can grow rapidly in shellfish subjected to ambient air conditions, such as during intertidal exposure. In this study, levels of total and pathogenic (tdh+/trh+) V. parahaemolyticus and total V. vulnificus were determined in oysters collected from two study locations where intertidal harvest practices are common. Samples were collected directly off intertidal flats, after exposure [ambient (Washington) or refrigerated (New Jersey)], and after re-immersion by natural tidal cycles. Samples were processed using an MPN-real-time PCR method for total and pathogenic V. parahaemolyticus, or V. vulnificus In Washington, mean levels of V. parahaemolyticus increased 1.38 log MPN/g following intertidal exposure and dropped 1.41 log MPN/g after re-immersion for one day, but was dependent upon the container type utilized. Pathogenic V. parahaemolyticus levels followed a similar trend. However, V. vulnificus levels increased 0.10 log MPN/g during intertidal exposure in Washington, but decreased by >1 log MPN/g after re-immersion. In New Jersey, initial levels of all vibrios studied were not significantly altered during the refrigerated sorting and containerizing process. However, there was an increase in levels after the first day of re-immersion by 0.79, 0.72, 0.92, and 0.71 log MPN/g for total, tdh+, trh+ V. parahaemolyticus, and V. vulnificus, respectively. Levels of all targets decreased to those similar to background after a second day of re-immersion. These data indicate that the intertidal harvest and handling practices for oysters that were studied in Washington and New Jersey do not increase the risk of illness from V. parahaemolyticus or V. vulnificus IMPORTANCE: Vibrio parahaemolyticus and Vibrio vulnificus are the leading causes of seafood-associated infectious morbidity and mortality in the United States. Vibrio spp. can grow rapidly in shellfish subjected to ambient air conditions, such as during periods of intertidal exposure. When oysters are submersed with the incoming tide, the vibrios can be purged. However, data on the rates of increase and purging during intertidal harvest is scarce, which limits the accuracy of risk assessments. The objective of this study was to help fill these data gaps by determining the levels of total and pathogenic (tdh+/trh+) V. parahaemolyticus and V. vulnificus in oysters from two locations where intertidal harvest practices are common, using the current industry practices. The data generated provides insight into the responses of Vibrio spp. of industry and public health relevant practices, which can be incorporated into risk management decisions.