Distribution of indicator bacteria and bacteriophages in shellfish and shellfish-growing waters

Shellfish (mussels and clams) and shellfish-growing waters were examined for indicator bacteria according to the EC regulations, Salmonella spp., coliphages and anti-Salmonella phages. Samples were collected both from natural-growing areas along the coast and from authorized shellfish-harvesting beds. The coastal area was affected by organic pollution and extensive faecal contamination and, according to the legal requirements, was unsuitable for shellfish farming. The shellfish collected along the coast also showed faecal contamination at levels which did not conform to legal standards. No significant differences were observed between the frequency of isolation of somatic coliphages and indicator bacteria from sea water. In contrast, both the authorized and wild coastal shellfish were contaminated by coliphages at a significantly higher level than the corresponding bacterial indicators for faecal contamination (chi 2 test, P < 0.01). Coliphage concentrations were significantly correlated with faecal indicators in marine waters (P < 0.001) and sediments (P < 0.05), but no correlation was found in shellfish, thus showing their low specificity as indicators of faecal pollution of human origin in shellfish of economic importance.