Global diversity and commonality of the antimicrobial resistome in activated sludge in wastewater treatment plants

Activated sludge in wastewater treatment plants (WWTPs) is a significant source and reservoir of antimicrobial resistance (AMR), potentially emanating from the human-associated sources into the environment through wastewater treatment effluent and biosolid applications. This study aimed to explore the global diversity and determinants of AMR within activated sludge. Metagenomic analysis of 181 samples from WWTPs in the USA, Europe, Japan, and China revealed a globally conserved set of antimicrobial resistance genes (ARGs) in activated sludge, distinct from those in wastewater. Notably, specific ARGs, such as AAC(6’)-Ib7, sul1, and qacEdelta1 were more abundant in activated sludge than in wastewater, suggesting that the selective growth of aerobic bacteria harboring these ARGs drives resistome formation. Furthermore, some ARGs associated with clinically important antimicrobials persisted from influent wastewater independent of microbial population dynamics. A strong correlation between ARG and mobile genetic element (MGE) abundances underscored the potential for ARG mobility within activated sludge.