Behavior of Escherichia coli and male-specific bacteriophage in environmentally contaminated bivalve molluscs before and after depuration

Abstract

We monitored the differential reduction rates and elimination patterns of Escherichia coli and male-specific (F ؉) bacteriophage during UV depuration 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 of E. coli by 90% was 6.5 h or less in all cases. In contrast, the amounts of time needed to reduce levels of F ؉ bacteriophage 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 sewage contamination were observed. Further experiments were conducted with mussels to determine the relative distributions of E. coli and F ؉ bacteriophage in tissue before and during depuration. Prior to depuration the majority of E. coli organisms (90.1%) and F ؉ bacteriophage (87.3%) were detected in the digestive tract (i.e., the digestive gland and intestine). E. coli and F ؉ bacteriophage were reduced in all tissues except the digestive gland to undetectable levels following depuration for 48 h. Within the digestive gland, levels of F ؉ bacteriophage were reduced to 30% of initial levels, whereas E. coli was reduced to undetectable levels. These results confirm previous laboratory studies showing the differential reductions of levels of E. coli and F ؉ bacteriophage during depuration. They also demonstrate that these differential elimination patterns are not affected by the duration of sewage contamination and that F ؉ bacteriophage are retained only in the digestive gland and are not sequestered into other internal tissues.

Localization of norovirus and poliovirus in Pacific oysters

“…Similarly, our report of PV IR in the gills of infected oysters is consistent with other studies that have used cell culture techniques to identify PV in experimentally infected oysters (Di Girolamo et al 1975). Dore and Lees (1995) also used cell culture to investigate tissue distribution of F+ bacteriophage in mussels (Mytilus edulis) and found that small amounts of F+ bacteriophage were detected in the labial palps and gills.…”

Heavy‐metal and microbial depuration of the clam Ruditapes decussatus and its effect on bivalve behavior and physiology

“…On the other hand, viruses and phages have been reported to survive in fish and shellfish tissue for months (Le Guyader et al, 2000). Shellfish harvested from moderately contaminated areas normally purge themselves of bacterial contaminants within 48 h, but these may be held up to 72 h in some circumstances (Dore and Lees, 1995). Bacterial reduction may be predominantly influenced by the digestive process, and it was assumed that a reduction in the levels of contaminants equates to elimination by defecation.…”

Viral contaminants of molluscan shellfish: detection and characterisation

“…FRNA phages in particular have been described as promising candidates to evaluate the virological quality of shellfish (Lees, 2000). Several studies have shown a correlation between the elimination kinetics of F+ RNA phages and those of enteric viruses (Dore and Lees, 1995;Power and Collins, 1989;Power and Collins, 1990). Nevertheless reports on discrepancies in the occurrences of FRNA phages and pathogenic viruses are frequent.…”