Occurrence of Vibrios in Frozen Seafoods and Survival of Psychrotrophic Vibrio cholerae in Broth and Shrimp Homogenate at Low Temperatures.

Pathogenic vibrios are important etiologic agents in tropical regions and have been frequently recovered from seafoods and aquacultured foods. In this study, commercially frozen seafoods including peeled shrimps and fish and shrimp dumplings were examined. Vibrio alginolyticus , Vibrio parahaemolyticus , Vibrio cholerae and Vibria fluvialis were recovered at 36.0%, 15.8%, 14.9% and 13.2%, respectively. A number of psychrotrophic vibrios were selected and their survival in tryptic soy broth (TSB) supplemented with 1% sodium chloride (NaCl) (TSBS medium) and shrimp homogenate at 4°C and -30°C were studied. Two psychrotrophic non-O1 V. cholerae (laboratory stocks no 128 and 129) survived well at these low temperatures. Counts decreased by about 1 log/ml in TSBS medium at 4°C for 6 days and 3 log/ml at -30°C for 3 days. Shrimp homogenate provided better protection than TSBS medium for psychrotrophic V. cholerae at -30°C. Survival of V. cholerae at low temperatures was further increased by the addition of 0.5% of heated pyrophosphate and metaphosphate, probably by decreasing the lethality of the cold injury to the cells. Measures should be taken to minimize the risk from pathogenic vibrios in frozen seafoods, especially if phosphates are used and psychrotrophic strains are present.