Occurrence of Vibrio spp. in fish and shellfish collected from the Swiss market

The genus Vibrio includes gram-negative bacteria that inhabit estuarine ecosystems. V. cholerae, V. parahaemolyticus, and V. vulnificus pose a considerable public health threat as agents of sporadic and epidemic foodborne infections associated with the consumption of raw or undercooked contaminated fish or shellfish. In this study, we analyzed 138 fish and shellfish samples collected from the Swiss market (fish fillets [n = 102], bivalves [n = 34], and squid [n = 2]). Microbiological analysis was done according to International Organization for Standardization method 21872-1/21872-2:2007, using thiosulfate citrate bile sucrose agar and chromID Vibrio agar as selective agar. Presumptive-positive colonies on thiosulfate citrate bile sucrose agar or chromID Vibrio agar were picked and were identified by the API 20E and species-specific PCR systems. V. cholerae isolates were tested further by PCR for the presence of the cholera toxin A subunit gene (ctxA). V. parahaemolyticus isolates were tested by PCR for genes encoding for thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). V. cholerae was isolated from three samples and V. parahaemolyticus from eight samples. None of these strains harbored species-specific virulence factors. Further, V. alginolyticus was isolated from 40 samples, and V. fluvialis was isolated from 1 sample. Our study provides, for the first time, data for the assessment of exposure to Vibrio spp. in raw fish and bivalves consumed in Switzerland.