Antibiotic contamination and antimicrobial resistance dynamics in the urban sewage microbiome in India.

The emergence and spread of antimicrobial resistance (AMR) in clinically important bacterial pathogens has severely compromised the effectiveness of commonly used antibiotics in healthcare. Acquisition and transmission of AMR genes (ARGs) are often facilitated by sublethal concentrations of antibiotics in microbially dense environments. In this study, we use sewage samples (n = 381) collected from six Indian states between June and December 2023 to assess the concentration of eleven antibiotics, microbial diversity, and ARG richness. We find antibiotics from seven drug classes and detect over 2000 bacterial amplicon sequence variants (ASVs). Metagenomic (n = 220) and isolated genome sequences (n = 305) of aerobic and anaerobic bacterial species identify 82 ARGs associated with 80 mobile genetic elements (MGEs). These MGEs are predominantly present in multidrug-resistant (MDR) bacterial pathogens. Comparative core genome analysis of MDR bacterial isolates (n = 7166) shows strong genetic similarity between sewage-derived strains and clinical pathogens. Our results highlight sewage as a significant reservoir for ARGs, where genetic exchanges occur and facilitate the evolution and spread of AMR pathogens in both community and healthcare settings. Additionally, the dipstick-based assay developed for ARGs detection can be used for sewage surveillance in low-resource settings for better understanding of resistance prevalence.