Fate and Proliferation of Vancomycin Resistance Genes in Two Typical Pharmaceutical Wastewater Treatment Plants

The emergence of vancomycin-resistant Enterococcus (VRE) and vancomycin resistance genes (VRGs) complicates the application of vancomycin, which is a last-line agent for human infectious diseases, and pharmaceutical wastewater treatment plants (PWWTPs) are widely thought to be important sources of corresponding antibiotic resistance genes (ARGs). In this study, two VRGs (vanA and vanB) were evaluated in two PWWTPs using quantitative polymerase chain reaction (qPCR) analysis to characterize the occurrence and fate of VRGs. The VRG concentration tended to decrease throughout all processing stages, while anaerobic treatment promoted the propagation of antibiotic-resistant bacteria and led to an increase in VRG abundance. Finally, the absolute concentrations of vanA and vanB exceeded 104 copies/mL in the effluents, and a significant amount of VRGs was transferred to sludge at 1.68 x 1017 copies/d. Redundancy analysis demonstrated that the relative abundance of ARGs was significantly correlated with the concentrations of vancomycin and COD. Furthermore, the relative abundance of vanA was increased in wastewater with multiple antibiotics, while the relative abundance of vanB only increased in the presence of vancomycin. This observation implied different intrinsic resistance mechanisms for different VRG subtypes. Overall, in this report, we describe the first comprehensive study on the fate and behavior of VRGs with different physicochemical or biochemical treatments and different antibiotic selection pressures in PWWTPs; this report provides important references for the environmental spread of VRGs.