Tetracycline Resistance Genes in Activated Sludge Wastewater Treatment Plants

The development and proliferation of antibiotic resistance in pathogenic, commensal, and environmental microorganisms is a major public health concern. The extent to which human activities contribute to the maintenance of environmental reservoirs of antibiotic resistance is poorly understood. In the current study, wastewater treatment plants (WWTPs) were investigated as possible sources of tetracycline resistance via qualitative and quantitative PCR (qPCR). Various WWTPs and two freshwater lakes were surveyed for the presence of an array of 10 tetracycline resistance determinants (tetR): tet(A)–(E), tet(G), tet(M), tet(O), tet(Q), tet(S). All WWTP samples contained more different types of tetR, as compared to the lake water samples. Gene copy numbers of tet(G) and tet(Q) in these samples were quantified via qPCR and normalized to both the volume of original sample and to the bacterial 16S rRNA gene copy number per sample (a proxy for bacterial abundance). Copies of tet(Q) were found to be highest in wastewater influent while tet(G) copies were highest in activated sludge. Investigation of the effects of UV disinfection on wastewater effluent showed no reduction in the number of detectable tetR types.