Transferable drug resistance in bacteria from fish-farm sediments

Antibiotic-resistant bacteria were isolated from sediment samples collected beneath two fish farms west of Bergen (Norway). The samples were collected just after the fish had been treated with oxytetracycline. Eighty-four bacterial isolates were tested for susceptibility to antibacterial agents. Most of the isolates were resistant to oxytetracycline, kanamycin, and sulfamethoxazole. Transferable plasmid-related resistance was shown by direct cell transfer and agarose gel electrophoresis. Among 34 multiple-resistant isolates, 7 isolates were able to transfer resistance to Escherichia coli HB101. Phenotypical characterization indicated that these seven isolates belonged to the genera Vibrio and Pseudomonas. The results indicate that sediments beneath fish farms may serve as a reservoir for transferable antimicrobial resistance genes.