Occurrence of super antibiotic resistance genes in the downstream of the Yangtze River in China: Prevalence and antibiotic resistance profiles.

The super antibiotic resistance genes (SARGs) demonstrate more severe threats than other antibiotic resistance genes while have not received enough attention in the environment. The study explored the prevalence and the antibiotic tolerance profiles of two typical SARGs, MCR-1 and NDM-1, and their hosting bacteria in the downstream of the Yangtze River and the nearby wastewater treatment plant (WWTP) and drinking water treatment plant (DWTP). Results indicated that MCR-1 and NDM-1 were prevalent in the influent and biological units of the WWTP. Their hosting bacteria were effectively removed, but 2.49 × 108 copies/L MCR-1 and 7.00 × 106 copies/L NDM-1 were still persistent in the effluent. In the Yangtze River, MCR-1 and NDM-1 were detected with higher abundance and antibiotic tolerance than the WWTP effluent and were significantly affected by nearby water contamination and human activities. In the DWTP, MCR-1 and NDM-1 were detected with average values 5.56 × 107 copies/L and 2.14 × 105 copies/L in the influent. Their hosting bacteria were undetectable in the effluent, but the two SARGs were still persistent with 1.39 × 107 copies/L and 6.29 × 104 copies/L, and were greatly enriched in the sludge. Molecular ecological networks demonstrated wide hosting relationships between MCR-1/NDM-1 and bacteria community in the DWTP. Redundancy analysis found that MCR-1 positively correlated with COD and NH3-N, while negatively correlated with turbidity. Additionally, MCR-1 hosting bacteria positively correlated with NO3--N and negatively correlated with COD and NH3-N. NDM-1 positively correlated with turbidity and NDM-1 hosting bacteria positively correlated with COD and NO2--N. The study demonstrated that the WWTP could not effectively remove SARGs with high amount of them being discharged into the Yangtze River. Then they were transported into the DWTP and the persistent SARGs in the effluent would probably be transferred into human, thus imposing great threats on public health.