Potentially pathogenic Aeromonas hydrophila organism were isolated from oysters frozen at −72°C for 1–1/2 years. The oysters which had been associated with 472 cases of gastroenteritis in Louisiana in November 1982, were examined and found negative for Salmonella, pathogenic Vibrio parahaemolyticus, and diarrhetic shellfish poison. In 1983, oysters from the same shellfish growing area in Louisiana were implicated in seven cases of gastroenteritis caused by A. hydrophila. The oysters collected in 1982 were reexamined and found to contain A. hydrophila (MPN 9.3/100 g). Twenty-three of 28 strains identified by the MICRO-IS and API-20E systems were positive for at least one of the tests for virulence which included the suckling mouse test, the adrenal Y-1 mouse cell test, and hemolysin assays. Of five strains tested, all showed activity in the rabbit ileal loop. Although these results do not prove that A. hydrophila caused the outbreak in 1982, they suggest that in cases of foodborne illness involving oysters, A. hydrophila should be included in the screening tests.

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Author notes

1Seafood Products Research Center.

2Food Research Laboratory.