Elimination of coliphages and Escherichia coll from mussels during depuration under varying conditions of temperature, salinity, and food availability

Abstract

Studies were undertaken to determine the effect of temperature, salinity, and food availability on the efficiencies of elimination of Escherichia coli and a 22-nm icosahedral coliphage from experimentally contaminated mussels. Test temperatures (5.5. 10, 16.5°C) and salinities (18.2, 28.6 ppt) reflected normal seasonal fluctuations during routine commercial depuration. The initial E. coli levels were reduced by >99% within 52 at all temperatures. In contrast, efficient coliphage elimination occurred at 16.5°C only. The initial E. coli levels were reduced by >99% at both salinities, while coliphage elimination was relatively inefficient under similar conditions. In unfiltered seawater, the addition or omission of food, in the form of Tetraselmis suecica, had no appreciable effect on either E. coli or coliphage elimination from mussels. In filter-clarified seawater, E. coli elimination was more efficient and coliphage elimination was considerably enhanced when food was added. In the absence of food, coliphage elimination was very inefficient. The results of these studies indicate that bacterial elimination from mussels during depuration is efficient through the range of parameters used. In contrast, coliphage elimination was generally inefficient throughout the study, suggesting that depuration, as currently practiced, cannot be relied upon to render mussels completely free of viral contamination. These studies emphasize that successful bacterial depuration does not reflect viral elimination and therefore, bacterial standards for efficient depuration of viruses are unreliable.