Urban aquatic systems as reservoirs and exposure pathways for resistant Escherichia coli in a South American river floodplain (Argentina).

Antimicrobial resistance (AMR) is a global concern with major implications for environmental health and human exposure, driven by antibiotic misuse, weak regulatory frameworks, and environmental dissemination. This study evaluated water quality and the presence of antibiotic-resistant Escherichia coli in surface waters and sediments surrounding Santa Fe City (Argentine Littoral Region), and assessed potential population exposure during recreational water activities. Among 684 strains (437 from water and 247 from sediments), 36.1% were resistant to at least one antibiotic. Resistance was frequently found to ampicillin, tetracycline, trimethoprim-sulfamethoxazole, ciprofloxacin, and colistin. Resistance to third-generation cephalosporins was detected at 40% of the study sites, including sites where extended-spectrum β-lactamase (ESBL)-producing strains were detected. Waste elimination sites, particularly those located in socioeconomically vulnerable urban areas, showed E. coli concentrations exceeding U.S. EPA recreational water quality standards and the highest proportions of multidrug-resistant strains, identifying these environments as hotspots of potential human exposure during water use. Although the exposure estimates represent a screening-level estimate of potential exposure rather than a quantitative infection risk assessment, they indicate that individuals could potentially ingest E. coli resistant to up to five antibiotic classes during a single swimming session at critical sites. Overall, these findings highlight urban aquatic ecosystems as important environmental settings for the occurrence of antimicrobial resistance and emphasize the relevance of recreational waters as potential exposure pathways within a One Health and environmental health management framework.