Properties of Pseudomonas enalia, a marine bacterium pathogenic for the invertebrate Crassostrea gigas (Thunberg)

Bacteriological investigations of dead and dying oysters in populations of Crassostrea gigas grown in Hood Canal, Oyster Bay, and Willapa Bay, Washington, were undertaken. Living, and presumably normal, oysters within the same sample set were also examined. Results indicated that the natural flora of Crassostrea gigas (Thunberg) is composed of organisms representing the genera Pseudomonas, Achromobacter, Flavobacterium, and Vibrio. Pollution indicator organisms such as Escherichia coli were not found. The flora of dead or dying oysters included a somewhat greater incidence of Pseudomonas sp.; a seawater-requiring organism isolated on several occasions from oyster gapers which had been collected from different geographical areas was identified as P. enalia. A description of the organism has been provided, and the characteristics are listed to facilitate identification by other workers encountering the organism in future studies of a similar kind. The seawater requirement exhibited by P. enalia was deduced to be a requirement for sodium chloride for growth of the organism. Experiments to determine the pathogenicity of Pseudomonas enalia were performed by use of experimentally infected animals maintained in aerated seawater tanks. Death of C. gigas occurred when the animal body tissue was injected with viable bacterial cell suspension. Results of histological studies of the normal and infected oyster tissue suggest that bacterial invasion of the tissue occurred.