Landfills as Hotspots of Multidrug Resistance Genes: Profiles, Drivers, and Hosts

The United Nations has identified municipal solid waste (MSW) landfills as significant reservoirs of antibiotic resistance genes (ARGs). Although ARG profiles, their primary drivers, and associated hosts have been well characterized in landfill leachate, such information remains limited for MSW landfills, which are the original source of the resistome. This knowledge gap impedes effective ARG monitoring at the source and poses challenges for public health management. Herein, we investigated the profiles of ARGs, their potential drivers, and associated hosts in refuse samples collected from a large-scale landfill using metagenomic sequencing and quantitative polymerase chain reaction analysis. Our findings revealed that landfills harbor diverse ARGs, with multidrug resistance genes (MDRGs) emerging as the dominant class, accounting for 39.78% of all ARGs detected. Notably, MDRGs exhibited high mobility potential (associated with plasmids, phages, and mobile genetic elements (MGEs)) and were frequently colocated with virulence factors. Pseudomonas, Acinetobacter, and Brevundimonas were identified as key MDRG hosts. Partial least-squares path modeling analysis indicated that MDRG variation was driven by multiple factors (i.e., MGEs, metal resistance genes (MRGs), hosts, and environmental factors). Additionally, metagenome-assembled genomes were found to carry multiple MDRGs. Collectively, these results underscore the role of landfills as critical hotspots for MDRGs.