Health significance of Gram‐negative bacteria associated with waste‐fed tropical aquaculture system

Commercially important freshwater fish species, Cyprinus carpio, Oreochromia niloticus, Sarother‐odon galilaeus and Clarias anguillaris grown in aquaculture ponds receiving untreated sewage and animal faecal waste and in an untreated concrete tank were sampled to determine the presence of potentially pathogenic Gram negative bacteria to man. The resistance of some representative bacterial isolates to some commonly used antibacterial drugs were also determined. Fourteen bacterial species from nine genera, namely, Escherichia, Citrobacter, Enterobacter, Proteus, Salmonella, Serratia, Klebsiella, Pseudomonas and Aeromonas from both fish intestinal tracts and culture water samples were identified. Escherichia coli predominated in the sewage and animal manure‐treated ponds, while fluorescent Pseudomonas were common in the untreated pond. Pathogenic Salmonella spp. were isolated at a low frequency (1.32%) in fish from the sewage pond. Of the 577 bacterial isolates identified, 199 (34.49%) were resistant to at least one antibacterial drug.