Occurrence of Vibrio spp. in blue mussels (Mytilus edulis) from the German Wadden Sea

The present study aimed at determining the contamination of blue mussels grown in Germany with relevant bacterial organisms. Seasonal variations were examined. For that purpose, mussel samples were taken regularly between June 2004 and May 2005 in seven shellfish-growing areas of the German Wadden Sea. A total of 90 samples were analysed. The analysis included the compulsory microbiological parameters Escherichia coli and Salmonella spp., as well as the determination of the contamination with Vibrio spp. Although the analysed mussels complied with the legislation in force, potential human pathogens were detected in a wide range of samples. Vibrio spp. was detected in 74.4% of the samples analysed in this study. Among Vibrio isolates, Vibrio alginolyticus was the species most frequently detected (51.2%), followed by Vibrio parahaemolyticus (39.5%). Vibrio vulnificus was detected in 3.5% of the samples. V. parahaemolyticus and V. vulnificus were not found in samples collected at low water temperatures. The results indicate that blue mussels from shellfish-growing areas in the German Wadden Sea regularly contain pathogens relevant to public health. They also show that E. coli is not a reliable indicator for the contamination with Vibrio spp. To improve consumer protection, it therefore seems necessary to extend the analysis of mussels for direct human consumption by additional parameters.