Metagenomic exploration of antibiotic resistome in treated wastewater effluents and their receiving water.

Environmental dissemination of antimicrobial resistance is a global health problem. Antimicrobial-resistant bacteria and antibiotic-resistant genes (ARGs) are constantly released into the environment through effluents (EFs) from wastewater treatment plants (WWTPs). Thus, requiring a better understanding of the selection and fate of ARGs in wastewater treatment processes. Therefore, we investigated the impacts of urban WWTP EFs on receiving water in the context of their resistomes and mobilomes. We used a HiSeq-based short read metagenomic approach to address the dynamics and diversity of ARGs in WWTP EF as well as the upstream (UP) and downstream (DN) river waters, followed by an investigation of plasmid-mediated ARGs. The abundance of ARGs at each site varied from 7.2 × 10 to 7.4 × 10 ARG copies per 16S rRNA gene copy, and EF samples showed the highest abundance, followed by DN and UP water samples. ARG diversity ranged from 121 to 686 types per site, and EF had the most diverse ARGs. Commonly identified ARGs in the EF and DN samples were clinically important and were absent in UP samples. The abundance of ARGs, mobile genetic elements (MGEs), and plasmid contigs found only in EF and DN were positively correlated with each other, indicating the importance of mobilomes in the dissemination of ARGs in the environment. Moreover, the proportions of plasmid-mediated ARGs was highest in the EF samples, followed by the DN and UP samples. These findings suggest that WWTP EF may act as a driving factor shaping the resistomes and mobilomes of receiving waters. In particular, a higher abundance of plasmid-mediated ARGs in WWTP EF suggests higher transmissibility in the DN environment.