Bacterial Flora of Cultrue-Oysters (Pacific Oyster, Crassostrea gigas)

Abstract

The present study was undertaken to analyse the bacterial flora of culture-oysters and of the silt accumulating on their shells. All the oysters were taken from two different areas of Hiroshima Bay during July and November, 1973, and the following January.
Enumeration and isolation of bacteria were conducted with a smear plate method using 50 percent seawater agar medium. Identification was based chiefly on the scheme of SHEWAN et al.
The generic composition of bacterial flora of the oysters differed from that of the marine water; that is, a very large portion of the isolates from the oysters consisted of genus Vibrio with no seasonal variation observed, while in the marine water pseudomonads were predominant. The ratio of psychrophilic vibrios to mesophilic ones, all isolated from the oyster samples, varied with the three seasons.
The bacterial flora of the silt was also composed mainly of vibrios, which were usually the same kind as those of the oysters.
The generic composition of the flora of commercial shucked oysters collected from some department stores in Tokyo in December, 1974, and the following January, was very similar to that of the culture-oysters.