Title: MICROBIAL FLORA OF PACIFIC OYSTERS (CRASSOSTREA

The microbial composition of Pacific oysters (Crassostrea gigas) subjected to UV-treated seawater was determined by quantitative and qualitative means. A total of 2, 779 microorganisms were identified from seawater and oysters during a 72 hour sampling period employing a computer assisted replica-plating technique. UV treatment effec^ tively eliminated coliforms and Pseudomonas Type I from seawater but other gram-negative asporogenous rods were more resistant. The microogranisms commonly found in oysters, whether subjected to UV-treated seawater or not, were, in the order of predominance, Pseudo-monas Type III or IV, Vibrio/Pseudomonas Type II, Flavobacterium / Cytophaga and Acinetobacter /Moraxella. The composition of microbial flora in oysters remained relatively stable irrespective of the microorganisms present in the seawater. A total of 18 pre-sumptive hemolytic vibrios were found in oysters but further confirma-tion revealed two isolates to be Vibrio parahaemolyticas and the remainder Aeromonas Species. Approximately 10 percent of the microorganisms isolated from seawater and oysters were gram-positive cocci and 14 to Z3 percent of these were coagulase positive, DNase positive, and (J-hemolytic on human blood agar