BEHAVIOR OF ESCHERICHIA-COLI AND MALE-SPECIFIC BACTERIOPHAGE IN ENVIRONMENTALLY CONTAMINATED BIVALVE MOLLUSKS BEFORE AND AFTER DEPURATION

We monitored the differential reduction rates and elimination patterns of Escherichia coli and male-specific (F+) bacteriophage during UV de puration for 48 h in oysters (Crassostrea gigas) and mussels (Mytilus edulis) contaminated by short-term (1 to 3 weeks) and long-term (more than 6 months) exposure to sewage in the marine environment. The time taken to reduce levels off. coli by 90% was 6.5 h or less in all cases . In contrast, the amounts of time needed to reduce levels of F+ bacte riophage by 90% were considerably longer: 47.3 and 41.3 h (after short - and long-term exposures, respectively) in mussels and 54.6 and 60.8 h (after short- and long-term exposures, respectively) in oysters. No differences in the rates of reduction of indicators of viral pollution following exposure of the shellfish to either short- or long-term sew age contamination were observed. Further experiments were conducted wi th mussels to determine the relative distributions of E. coli and F+ b acteriophage in tissue before and during depuration. Prior to depurati on the majority of E. coli organisms (90.1%) and F+ bacteriophage (87. 3%) were detected in the digestive tract (i,e., the digestive gland an d intestine), E. coli and F+ bacteriophage were reduced in all tissues except the digestive gland to undetectable levels following depuratio n for 48 h. Within the digestive gland, levels of F+ bacteriophage wer e reduced to 30% of initial levels, whereas E. coli was reduced to und etectable levels, These results confirm previous laboratory studies sh owing the differential reductions of levels of E. coli and F+ bacterio phage during depuration. They also demonstrate that these differential elimination patterns are not affected by the duration of sewage conta mination and that F+ bacteriophage are retained only in the digestive gland and are not sequestered into other internal tissues.