Extended-Spectrum β-Lactamase and Carbapenemase Genes are Substantially and Sequentially Reduced during Conveyance and Treatment of Urban Sewage

Urban wastewater systems (UWSs) are a main receptacle of excreted antibiotic resistance genes (ARGs) and their host microorganisms. However, we lack integrated and quantitative observations of the occurrence of ARGs in the UWS to characterize the sources and identify processes that contribute to their fate. We sampled the UWSs from three medium-size cities in Denmark, Spain, and the United Kingdom and quantified 70 clinically important extended-spectrum beta-lactamase and carbapenemase genes along with the mobile genetic elements and microbial communities. Results from all three countries showed that sewage-especially from hospitals-carried substantial loads of ARGs (10(6)-10(7) copies per person equivalent), but these loads progressively declined along sewers and through sewage treatment plants, resulting in minimal emissions (10(1)-10(4) copies per person equivalent). Removal was primarily during sewage conveyance (65 +/- 36%) rather than within sewage treatment (34 +/- 23%). The extended-spectrum beta-lactamase and carbapenemase genes were clustered in groups based on their persistence in the UWS compartments. The less-persistent groups were associated to putative host taxa (especially Enterobacteriaceae and Moraxellaceae), while the more persistent groups appeared horizontally transferred and correlated significantly with total cell numbers and mobile genetic elements. This documentation of a substantial ARG reduction during sewage conveyance provides opportunities for antibiotic resistance management and a caution for sewage-based antibiotic resistance surveillance.

Automated summary

The study of urban wastewater systems in Denmark, Spain, and the UK revealed a significant reduction in antibiotic resistance genes during sewage conveyance, presenting opportunities for antibiotic resistance management and caution for surveillance based on sewage.