Discharge of KPC-2 genes from the WWTPs contributed to their enriched abundance in the receiving river.

At present, very little is known about the persistence and spread pathway of KPC-2 genes in the environment. Our previous study reported the prevalence and persistence of KPC-2 genes in wastewater treatment plants (WWTPs). In the present work, we investigated the occurrence and fate of KPC-2 genes in a WWTP discharge-receiving river and studied the effect of WWTP discharges on the prevalence of KPC-2 genes and host bacteria in the receiving river. It is observed that a considerable level of KPC-2 genes occurred in the receiving river, and a significant increase of bla abundance in the downstream following WWTP discharge was observed compared to the upstream. Furthermore, opportunistic pathogens with 100% identical bla sequence, like Escherichia coli and Kluyvera georgiana, were isolated from both WWTP and its receiving water, whereas no bla carrying bacteria was detected in the upstream. These findings indicated that the treated wastewater discharges have a considerable influence on bla levels in the receiving river. Interestingly, there is no correlation between concentrations of antibiotics and bla concentrations, demonstrating that the increase of KPC-2 genes in the receiving river is mainly due to WWTP release. This finding is important because it illustrates a significant pathway for KPC-2 gene proliferation to the environment.