Clostridium perfringens as an Indicator of Hygienic Quality of Depurated Shellfish.

A comparison of the recoveries of Clostridium perfringens , Escherichia coli and Streptococcus faecalis from naturally and artificially contaminated mussels and oysters was made. Only C. perfringens was regularly recovered from naturally contaminated shellfish. Laboratory studies showed that this was due to C. perfringens spores retaining viability significantly longer than vegetative cells of the other organisms tested, under marine conditions. Over 97% of presumptive C. perfringens colonies were confirmed as positive. A survey of mussels at 24 sites, over ca. 60 km of coastline, found C. perfringens at 23 but E. coli at only two of the sites. Therefore, enumeration of C. perfringens can indicate fecal pollution where enumeration of E. coli shows none. Also, confirmation of presumptive colonies may not be required, rendering enumeration more rapid. Despite the greater persistence of C. perfringens spores, studies in a commercial depuration tank showed that oysters were cleansed to an acceptable level using a standard 48-h immersion. Depuration was found to be essential because all three organisms tested survived for a considerable period of time in oysters stored dry at 4°C, which is normal commercial practice.