The Fate of Tetracycline Resistant Bacteria in Wastewater Treatment Plants as a Function of Operating Characteristics

The overall goals of this study were 1) to monitor the abundance and distribution of tetracycline resistant bacteria (TRB) and several tetracycline resistance genes (TRG) in three full scale wastewater treatment plants (WWTP) and 2) to develop a mathematical model to describe the ‘carrying capacity’ of a given wastewater treatment plant for resistant bacteria. Irrespective the mode of operation or physical location of the WWTPs, significant amounts of tetracycline resistant bacteria (101 to103 CFU/mL) and tetracycline resistance genes (105to107 copies/mL) were discharged into the receiving water even after disinfection. Notably, the percentage of tetracycline resistant bacteria increased upon ultraviolet (UV) disinfection compared to chlorination or no disinfection. Of the seven tetracycline resistance genes tested, tetracycline resistance ribosomal protection genes, especially tet(O) and tet(W) were more abundantly detected than tetracycline resistance efflux genes [tet(A, B, C)] in WWTPs. Using the developed model, it was inferred that the WWTP operating conditions strongly influenced their net TRB “carrying capacity”