Microbial flora of Pacific oysters (Crassostrea gigas) subjected to UV-irradiated seawater

Graduation date: 1971The microbial composition of Pacific oysters (Crassostrea gigas)\ud subjected to UV-treated seawater was determined by quantitative and\ud qualitative means. A total of 2,779 microorganisms were identified\ud from seawater and oysters during a 72 hour sampling period employing\ud a computer assisted replica-plating technique. UV treatment effectively eliminated coliforms and Pseudomonas Type I from seawater\ud but other gram-negative asporogenous rods were more resistant. The\ud microogranisms commonly found in oysters, whether subjected to UV-treated\ud seawater or not, were, in the order of predominance, Pseudomonas\ud Type III or IV, Vibrio/Pseudomonas Type II, Flavobacterium/\ud Cytophaga and Acinetobacter /Moraxella. The composition of\ud microbial flora in oysters remained relatively stable irrespective of\ud the microorganisms present in the seawater. A total of 18 presumptive\ud hemolytic vibrios were found in oysters but further confirmation\ud revealed two isolates to be Vibrio parahaemolyticas and the remainder Aeromonas species. Approximately 10 percent of the\ud microorganisms isolated from seawater and oysters were gram-positive\ud cocci and 14 to 23 percent of these were coagulase positive,\ud DNase positive, and (β-hemolytic on human blood agar