P-034. Reduction of Vibrio vulnificus Numbers in Oysters Using a Flow-Through Depuration System

R. Wood, S. Rikard, Y. Brady, R. Wallace, C. R. Arias;
Auburn Univ., Auburn, AL.

Background: Vibrio vulnificus remains the main concern for the oyster industry in the Gulf coast. Several measures have been implemented by the oyster industry in order to ensure consumer safety. The most effective ones include post-harvest treatments such as high hydrostatic pressure processing, cold temperature pasteurization and freezing. Although all these methodologies reduce V. vulnificus to non-detectable levels, there is still a high demand of raw oysters by consumers. Some decontamination techniques such as relaying and depuration have been tried in order to eliminate oyster-borne pathogens. However, experiments on depuration of V. vulnificus from oysters showed conflicted results. Most of those depuration methods were based on recirculating systems. The objective of our study was to test the efficacy of a flow-through depuration system to eliminate V. vulnificus from oysters. Methods: One year old oysters were kept in 1000L raceways at the Auburn University Shellfish Laboratory at Dauphin Island, AL. Seawater was pumped in from the Gulf of Mexico at a rate of 3L/min. The water was 100µm filtered and UV sterilized. Water temperature and salinity were measured twice daily. The oysters remained in this depuration system (U.S. Provisional Patent Application No. 60/962,535) for 7 days. Samples were taken daily. Oyster meat was homogenized, diluted and plated to determine total bacterial and V. vulnificus counts using a gene probe according to FDA protocols. Results: At time 0 total bacterial counts were 2x105 CFU/g while V. vulnificus numbers were around 2x103CFU/g. A sharp drop in bacterial numbers was observed after two days followed by a steady decline till the end of the experiment. After seven days depurating, total bacterial counts were 3x103cfu/g and V. vulnificus numbers fell by one to two orders of magnitude from starting levels. Repetition of the experiment on two other occasions gave similar results.