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 blaKPC-2 abundance in the downstream following WWTP discharge was observed compared to the upstream. Furthermore, opportunistic pathogens with 100% identical blaKPC-2 sequence, like Escherichia coli and Kluyvera georgiana, were isolated from both WWTP and its receiving water, whereas no blaKPC-2 carrying bacteria was detected in the upstream. These findings indicated that the treated wastewater discharges have a considerable influence on blaKPC-2 levels in the receiving river. Interestingly, there is no correlation between concentrations of antibiotics and blaKPC-2 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.