Effects of refrigeration and alcohol on the load of Aeromonas hydrophila in oysters

Abstract

Members of the bacterial genus Aeromonas are widely distributed throughout the environment and are readily cultured from a variety of foods. One member of this genus, Aeromonas hydrophila, has been reputed to be a significant cause of gastrointestinal disease. In this study, we examined the effects of refrigeration and alcohol on the level of A. hydrophila in oysters. Specifically, vodka was examined because it is used by the food service industry in preparation of Oysters Romaaoff. One set of oysters was shucked on receipt, whereas others were refrigerated intact for 7 days at 5°C. The oysters were blended and the numbers of A. hydrophila present determined using starch ampicillin agar. Oysters were also shucked and placed on the half shell with 5 ml of vodka for 10 min. The oysters were then washed and presumptive A. hydrophila levels determined in both the washate and homogenate. On the day of purchase, the average number of presumptive A. hydrophila found was 7.6 x 104 CFU/g of oyster meat. After 7 days of refrigeration, the average number had increased to 3.2 x 105 CFU/g of oyster meat. In the oysters treated with vodka, the average number of A. hydrophila present internally was 9.9 x 104 with high numbers (103 to 104) isolated from the oyster surface. From these data, it is clear that refrigeration and alcohol treatment are not sufficient to reduce loads of A. hydrophila in or on oysters.