Effect of chilling and freezing on survival of Vibrio parahaemolyticus on fish fillets

Vibrio parahaemolyticus is a foodborne pathogen isolated from coastal waters of the United States, and from seafoods including fish. No information is available on the viability of V. parahaemolyticus on raw, chilled and frozen fish. A three-strain mixture of V. parahaemolyticus was inoculated on fish fillets (pH 6 4) to obtain a bacterial load of 10(4) (high) or 10(3) (low) CFU/fillet, and stored at 4C or 8C for 9 days or at -18C for seven weeks. At 4C and 8C, and at both levels of inoculation, V. parahaemolyticus survived on the fillets for the entire duration of the study. However, there was a significant reduction (P<0.01) in V. parahaemolyticus population on the fillets by 9 days of storage. In the frozen fillets, there was a sharp decline (P<0.01) in the population of V. parahaemolyticus by day 5 of storage. Although chilling and freezing significantly (P<0.01) inactivated high numbers of V. parahaemolyticus on fish, they cannot be relied upon as a method to reduce V. parahaemolyticus on fish, since the time and magnitude of reduction depends on the initial load of the pathogen and the storage temperature.