Occurrence of Bacterial Pathogens and Human Noroviruses in Shellfish-Harvesting Areas and Their Catchments in France

Abstract

During a 2-year study, the presence of human pathogenic bacteria and noroviruses was investigated in shellfish, seawater and/or surface sediments collected from three French coastal shellfish-harvesting areas as well as in freshwaters from the corresponding upstream catchments. Bacteria isolated from these samples were further analyzed. <i>Escherichia coli</i> isolates classified into the phylogenetic groups B2, or D and enterococci from <i>Enterococcus faecalis</i> and <i>E. faecium</i> species were tested for the presence of virulence genes and for antimicrobial susceptibility. <i>Salmonella</i> members were serotyped and the most abundant serovars (Typhimurium and its monophasic variants and Mbandaka) were genetically characterized by high discriminative subtyping methods. <i>Campylobacter</i> and <i>Vibrio</i> were identified at the species level, and haemolysin-producing <i>Vibrio parahaemolyticus</i> were searched by <i>tdh</i>- and <i>trh</i>- gene detection. Main results showed a low prevalence of <i>Salmonella</i> in shellfish samples where only members of <i>S.</i> Mbandaka were found. <i>Campylobacter</i> were more frequently isolated than <i>Salmonella</i> and a different distribution of <i>Campylobacter</i> species was observed in shellfish compared to rivers, strongly suggesting possible additional inputs of bacteria. Statistical associations between enteric bacteria, human noroviruses (HuNoVs) and concentration of fecal indicator bacteria revealed that the presence of <i>Salmonella</i> was correlated with that of <i>Campylobacter jejuni</i> and/or <i>C. coli</i> as well as to <i>E. coli</i> concentration. A positive correlation was also found between the presence of <i>C. lari</i> and the detection of HuNoVs. This study highlights the importance of simultaneous detection and characterization of enteric and marine pathogenic bacteria and human noroviruses not only in shellfish but also in catchment waters for a hazard assessment associated with microbial contamination of shellfish.