[Microbiological monitoring of mussels and clams collected from the shellfish-growing marine areas in Rimini Province]. / Monitoraggio microbiologico di mitili e vongole raccolti da aree di mare adibite a molluschicoltura della Provincia di Rimini.

A 5 years survey (1996-2000) was performed on the microbiological quality of shellfish (mussels and clams) collected from authorized shellfish-growing area of the North Adriatic Sea (province of Rimini). 7.0% of mussel samples (33/474) and 21.9% of clam samples (218/996) exceeded the legal limits for faecal indicators (Dlgs 530/92). The faecal contamination of shellfish was related to the organic pollution arriving from inland surface waters. In fact shellfish harvested near the coast were more contaminated, as well as shellfish grown in the surface layers of the open sea, where the fresh waters of the streams tend to stratify. Faecal contamination was also directly correlated with rainfall, probably because the atmospheric precipitation, increasing the flow of the streams, favoured the transport of organic substances and micro-organisms deriving from the soil washing and the municipal sewage effluents. Furthermore, when rainfall was particularly plentiful, sewage inflow could also exceed the hydraulic capacity of the treatment plants; thus making necessary to discharge untreated waste directly into surface waters. Salmonellae were found in 0.7% of clam samples. Although this percentage is very low, it shows that pathogenic micro-organisms are present in this area of sea. This finding, together with the high variability of shellfish pollution due to occasional factors as rainfall, emphasise the importance of the systematic monitoring of the microbiological quality of shellfish.

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.