Abundance and distribution of tetracycline resistance genes in freshwater aquaculture facilities

We investigated the occurrence and abundance of tetracycline resistance genes (tet^R) in four aquaculture facilities with contrasting OTC treatment histories. End-point and real-time polymerase chain reaction methods were used to detect and quantify tet^R genes in water, sediment and feed samples collected from the four aquaculture facilities. Effluent water samples had markedly higher tet^R gene concentrations than did corresponding influent samples (3- to 50-fold higher). Tet^R concentrations in sedimentation pond samples were higher in control facilities than in treatment facilities (5- to 600-fold higher). Surprisingly, unmedicated feed contained substantial concentrations of all genes, but medicated feed had significantly higher tet^R levels than unmedicated feed (1- to 40-fold higher). OTC concentrations were quantified for each of these matrices and were compared to the corresponding tet^R concentrations. This study has important implications for the management of aquaculture activities and underscores the need to further evaluate potential environmental reservoirs of antibiotic resistance.