Background: Antibiotic-resistant pathogens are challenging treatment of infections worldwide. Urban sewage is potentially a major conduit for dissemination of antibiotic resistance genes into various environmental compartments. However, the diversity and abundance of such genes in wastewater are not well known.

Methods: Here, seasonal and geographical distributions of antibiotic resistance genes and their host bacterial communities from Chinese urban sewage were characterized, using metagenomic analyses and 16S rRNA gene-based Illumina sequencing, respectively.

Results: In total, 381 different resistance genes were detected, and these genes were extensively shared across China, with no geographical clustering. Seasonal variation in abundance of resistance genes was observed, with average concentrations of 3.27 × 10¹¹ and 1.79 × 10¹² copies/L in summer and winter, respectively. Bacterial communities did not exhibit geographical clusters, but did show a significant distance-decay relationship (P < 0.01). The core, shared resistome accounted for 57.7% of the total resistance genes, and was significantly associated with the core microbial community (P < 0.01). The core human gut microbiota was also strongly associated with the shared resistome, demonstrating the potential contribution of human gut microbiota to the dissemination of resistance elements via sewage disposal.

Conclusions: This study provides a baseline for investigating environmental dissemination of resistance elements and raises the possibility of using the abundance of resistance genes in sewage as a tool for antibiotic stewardship.