Effect of temperature on uptake and survival of Vibrio parahaemolyticus in oysters (Crassostrea plicatula).

ABSTRACT

This study investigated accumulation of Vibrio parahaemolyticus in Zhe oyster (Crassostrea plicatula) from culture water and effectiveness of frozen and chilled storage on reducing V. parahaemolyticus in oysters. Freshly harvested oysters were placed in artificial seawater containing V. parahaemolyticus (10(4)CFU/mL) at 16, 20, 26, and 32 degrees C for 96 h. Contaminated oysters were stored at chilled temperatures (0, 5, and 15 degrees C) and frozen at -18 and -30 degrees C and changes of V. parahaemolyticus populations in oysters were determined using the most probable number (MPN) method. Accumulations of V. parahaemolyticus in C. plicatula reached the peaks at 6.66 (32 degrees C), 5.72 (26 degrees C), 5.04 (20 degrees C), 4.72 (16 degrees C) log MPN/g after 32 h in contaminated artificial seawater. Holding contaminated Zhe oysters at 5 and 0 degrees C reduced V. parahaemolyticus populations in both shell stock and shucked oysters. Populations of V. parahaemolyticus in shell stock and shucked oysters declined by 1.42 and 2.0 log MPN/g, respectively, after 96 h of storage at 5 degrees C and by 2.11 and 2.38 log MPN/g, respectively, after 96 h of storage at 0 degrees C. However, populations of V. parahaemolyticus increased by 2.44 log MPN/g in shell stock oysters and by 1.64 og MPN/g in shucked oysters when stored at 15 degrees C for 60 h. Frozen storage was effective in inactivating V. parahaemolyticus. Populations of V. parahaemolyticus in shell stock and shucked oysters decreased from 5.46log MPN/g to 1.66 and 0.38 log MPN/g, respectively, after 75 days of storage at -30 degrees C. No V. parahaemolyticus cells were detected (<3 log MPN/g) in the shucked oysters after 60 days of storage at -18 degrees C. These results demonstrated that accumulation of V. parahaemolyticus in cultured C. plicatula increases as water temperature increases. Harvested C. plicatula should be stored at 5 degrees C or lower to control the hazard of V. parahaemolyticus.