Transferable drug-resistant coliforms in fish exposed to sewage

. In this study, the thermotolerent fecal coliform (Th FC) bacterial population (n = 81) in a waste-fed aquaculture system was examined for multiple antibiotic resistance and the possession of transferable drug resistance factors (R factors). Multiple antibiotic resistant (MAR) coliforms were found to be common in the sewage-fed pond environment, with 83% of the screened MAR isolates harboring plasmids of > 10 kilo base pair (kb). The transfer of resistance was confirmed by mating experiments in 92% of plasmid-positive MAR coliforms with a nalidixic acid (NA) resistant strain, Escherichia coli ATCC (American Tissue Type Cell Culture) 14948 recipient in the presence of DNase (Deoxyribonuclease). Antibiotic resistance profiles of some mated progenies (70.83%) indicated that transfer was unidirectional. DNase-treated cell-free supernatants did not transform, which excluded transduction. A DNase-resistant conjugation-like mechanism probably plays a major role in the transfer of resistance factors. Physical evidence of transmissible resistance factors in fish suggests a potential health risk to humans and animals, including farmed fish.