Isolation of Staphylococcus aureus from Raw Fish in Relation with Culture Methods

概要

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Five hundred and fifty fish samples from various stages in the course of distributions in Hyogo prefecture (209 retailed in super markets, 173 obtained from fishery cooperatives at the harbor, 91 caught by trawling, and 77 caught by rod fishing) were examined for contamination with Staphylococcus aureus (S. aureus). S. aureus was detected in 41 (19.6%) of the retail fish samples and 46 (26.6%) of the samples from the fishery cooperatives. No S. aureus was isolated from the living fish (91 trawled and 77 fished by rod). With regard to the retail fish, the contamination rate of processed fish (26.0%) was significantly higher than that of unprocessed (14.2%). For 88 samples, the efficacy of the selective medium was compared using Baird-Parker agar and mannitol salt agar supplemented with egg yolk (MSEY agar) by the direct plate and enrichment culture methods. Using the direct culture method, the S. aureus positive rate with the Baird-Parker agar (30.7%) was significantly higher (P<0.01) than that with the MSEY agar (6.8%). The enrichment culture method remarkably raised the S. aureus detection rate. Seventy-eight (85.7%) of ninety-one isolates belonged to the Human ecovar. Sixty-two (68.1%) of the ninety-one isolates had some enterotoxin genes, including 44 (48.4%) with the sea gene. These data showed that fish was contaminated with S. aureus after landing and Baird-Parker agar had an advantage in detecting S. aureus with a direct plate culture.