Faecal contamination of echinoderms: first report of heavy Escherichia coli loading of sea urchins from a natural growing area.

UNLABELLED: Although little evidence existed to support that view, European countries and in particular France, have regarded echinoderms, including sea urchins, as low risk in terms of feacal contamination. It is hypothesized that the sea urchins mode of feeding, which is based on grazing and differs from bivalve molluscs, would prevent it from concentrating high levels of Escherichia coli. Here, we monitored E. coli levels in sea urchins (Paracentrotus lividus) and in filter-feeder mussels (Mytillus galloprovincialis), collected concurrently from the same natural area over a 1-year period to verify this assumption. Sea urchins were collected on the seafloor, whereas mussels were collected from the water column at a depth of 4 m. Our results showed heavy bacterial loading of sea urchins in a natural growing environment. Moreover, we highlighted that E. coli contamination of sea urchins could, in certain conditions, be higher than those detected in filter-feeding mussels collected at the same location. Finally, the results showed a significant correlation between rainfall and E. coli concentrations in sea urchins, suggesting that the bacterial safety of sea urchin could be linked to the quality of the surrounding water. SIGNIFICANCE AND IMPACT OF THE STUDY: The European regulation requires competent authorities to monitor the sanitary status of shellfish, including live echinoderms, through faecal indicator organisms. In the French Mediterranean, sea urchin production is significant. Until now, as no data showed significant E. coli contamination levels, no monitoring programs focused on this species. This study demonstrates that sea urchins are more vulnerable to faecal contamination than previously hypothesized, especially during heavy rainfall. In consequence, the European authority general approach to microbiological management of shellfish should be applied to sea urchins.