Antibiotic resistome in a landfill leachate treatment plant and effluent-receiving river

Landfills leachate contained diverse antibiotic resistance genes (ARGs). Treated landfill leachate effluent could enter into the downstream environments, leading to the dissemination of ARGs, which might pose a health risk to public. Here, we used high-throughput qPCR to characterize the resistome and 16S rRNA-based Illumina sequencing to analyze the bacterial community in a leachate treatment plant and the river near the landfill. A total of 91 ARGs and 5 mobile genetic elements were detected. Leachate treatment process significantly changed the profiles of resistome and bacterial community structures. Similar bacterial community structure and ARG profiles were detected between effluent and downstream river, which were both dominated by multidrug and beta-lactams resistance genes and harbored higher ARG relative abundance than that in upstream river. In particular, seven ARGs were detected both in effluent and downstream river samples but not detected in upstream river, including genes encoding resistance to vancomycin (vanXD and vanSB) and carbapenem (cphA and blaGES), which implied the effects of the effluent on its receiving river. This study highlights the risk of discharge of processed landfill leachate in dissemination of antibiotic resistance determinants to the environments, and suggests an urgent need for surveillance of ARGs and development of techniques to mitigate the risk.