Antimicrobial resistome and mobilome in the urban river affected by combined sewer overflows and wastewater treatment effluent

Abstract

The dissemination of antimicrobial resistance in the environment is an emerging global health problem. Wastewater treatment effluent and combined sewer overflows (CSOs) are major sources of antimicrobial resistance in urban rivers. This study aimed to clarify the effect of municipal wastewater treatment effluent and CSO on antimicrobial resistance genes (ARGs), mobile gene elements, and the microbial community in an urban river. The ARG abundance per 16S-based microbial population in the target river was 0.37–0.54 and 0.030–0.097 during the CSO event and dry weather, respectively. During the CSO event, the antimicrobial resistome in the river shifted toward a higher abundance of ARGs to clinically important drug classes, including macrolide, fluoroquinolone, and β-lactam, whereas ARGs to sulfonamide and multidrug by efflux pump were relatively abundant in dry weather. The abundance of intI1 and tnpA genes were highly associated with the total ARG abundance, suggesting their potential application as an indicator for estimating resistome contamination. Increase of prophage during the CSO event suggested that impact of CSO has a greater potential for horizontal gene transfer (HGT) via transduction. Consequently, CSO not only increases the abundance of ARGs to clinically important antimicrobials but also possibly enhances potential of HGT in urban rivers. HIGHLIGHTS CSO substantially increased abundance of ARG and MGE in river water.; Anaerobic microbes in CSO harbored ARGs to β-lactam, macrolide, and quinolones.; Transduction could play an important role in ARG propagation after CSO.; intI1 and tnpA genes exhibited a higher correlation with total ARG abundance.;

Keywords

• antimicrobial resistance gene
• combined sewer overflow
• microbial community
• mobile genetic element
• shotgun metagenomic sequencing
• wastewater treatment plant