Occurrence of Tetracycline Resistance Genes in Aquaculture Facilities with Varying Use of Oxytetracycline
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The contribution of human activities to environmental reservoirs of antibiotic resistance is poorly understood. The purpose of this study was to determine if oxytetracycline (OTC) use in aquaculture facilities increased the detection frequency (i.e., prevalence) of tetracycline resistance (tetR) genes relative to facilities with no recent OTC treatment. We used polymerase chain reaction to screen water and sediment from four noncommercial fish farms in northwestern Wisconsin for the presence of ten tetR determinants: tet(A), tet(B), tet(D), tet(E), tet(G), tet(M), tet(O), tet(Q), tet(S), and tet(W). Water from farms with recent OTC use had significantly higher tetR detection frequencies than did water from farms without recent OTC use, with prevalence in raceways and rearing ponds of farms with recent OTC use exceeding by more than twofold that of farms not using OTC. Effluent from all farms, regardless of treatment regime, had higher tetR detection frequencies than their corresponding influent for all genes, but the specific combinations of tetR genes detected in a sample were not different from their corresponding influent. Although OTC use was associated with the increased occurrence and diversity of tetR genes in water samples, it was not found to relate to tetR gene occurrence in sediment samples. Sediment samples from facilities with no recent OTC use had significantly higher frequencies of tetR gene detection than did samples from facilities with recent OTC use. All of the tetR genes were detected in both the medicated and nonmedicated feed samples analyzed in this study. These findings suggest that both OTC treatment in aquaculture facilities and the farms themselves may be sources of tetR gene introduction to the environment. To our knowledge, this is the first study to use genotypic and cultivation-independent methods to examine tetR gene occurrence associated with OTC use in aquaculture.
KeywordsSediment Sample Antibiotic Resistance Gene Detection Frequency Feed Sample Influent Water
We thank Roderick Mackie and Satoshi Koike for kindly providing positive controls for tetR gene amplification. We also thank Trevor Ghylin, Ashley Shade, and Stuart Jones for helping collect the samples and for the discussions and Azivy Che Aziz, Aaron Jones, and Emma Ingebretsen for the help with processing the samples. This research was funded by a grant from Wisconsin SeaGrant (R/AQ-40) to K.D.M and J.A.P.
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