Microbial flora and level of Vibrio parahaemolyticus of oysters (Crassostrea virginica), water and sediment from Galveston Bay.

Aerobic plate counts at 25 C of freshly harvested oysters ranged from 2.3 X 10 exp 4 to 3.0 X 10 exp 7 and those of sediment samples from <10 exp 2 to 3.0 X 10 exp 6/g. Counts of water samples were nearly always <10 exp 2/ml. Vibrio, Aeromonas, and Moraxella species predominated in the fresh oysters. Vibrio parahaemolyticus was isolated from 39 of 66 oyster samples and from 9 of 20 sediment and water samples. Isolation was most effective with prior enrichment of samples in trypticase soy broth with 7% NaCl and subsequent plating on thiosulfate citrate bile salts sucrose agar. V. parahaemolyticus was detected in only 1 of 8 refrigerated retail oyster samples. Aerobic plate counts at 25 C of refrigerated retail oyster were not much different from those of similar lots shucked under asceptic conditions in the laboratory (before shucking and washing in plants). Aeromonas and Moraxella species were predominant in oysters at retail level.