Marine

The effects of fish farming on bacterial density, biomass, community structure, and their possible link to antibiotic resistance have been investigated in coastal sediments of the Ligurian Sea (Western Mediterranean).

The top 2 cm of the sediment under a fish farm and control areas were analyzed during summer 2000. Bacterial density and biomass were three folds higher (up to 3×1010 cells/g and in sediments beneath the fish cages compared to the control sediments. The number of Colony Forming Units (CFUs) for culturable bacteria and microbiological investigations indicated a shift in the relative importance of the Gram-negative bacteria in impacted sediments.

Gram-positive bacteria increased their relevance in the control site where they represented up to 90% of total isolates. Antibiotic sensitivity tests showed a high percentage of resistant strains in both control and impacted sediments, which indicates widespread antibiotic resistance within bacterial populations in areas surrounding fish farms.

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