The accumulation of the indicator bacteria Escherichia coli in mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis) under experimental conditions

Abstract

       The simultaneous effects of temperature and salinity on the accumulation of Escherichia coli (E. coli) in mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis) were studied under experimental conditions with different concentrations of E. coli in seawater. The experiments were carried out in 3000 L tanks, within the natural range of temperature (12^oC, 18^oC and 24^oC) and salinity (32 psu and 37 psu) in the coastal areas of the Adriatic Sea. Within the achieved range of E. coli concentrations in seawater (4x10-4.6x10³ CFU/100 ml), bacteria accumulated rapidly in the bivalves, reaching the highest concentrations (plateau) after 1 h in mussels and 2 h in oysters. Under the same concentrations of E. coli in seawater, a significantly higher plateau was reached in mussels than oysters. Significant correlations between the E. coli concentration in seawater and bivalves (CR; concentration ratio) were found. The results clearly showed that CR was controlled by temperature and salinity of seawater. Changes in temperature had a strong effect on CR fluctuation, whereas in oysters an effect of changes in salinity on CR variation was also found only in oysters. The interaction between temperature and salinity was statistically significant and suggested that their simultaneous effects on CR were significantly greater than when each of these factors acted independently. The highest E. coli concentrations in mussels and oysters exceeded the concentrations in seawater by an order of magnitude at least, while the CR in mussels exceeded the CR in oysters by 7.7- to 38.5-fold.