Spatial variation in antibiotic resistant Escherichia coli in surface waters across Northern Ireland

Antimicrobial resistance (AMR) is a growing global health crisis, it also presents distinct regional challenges driven by differences in local environment, population and antibiotic usage. In Northern Ireland data on AMR in bathing waters remains limited and current water quality legislation does not require AMR monitoring.
Surface water samples were collected from Newcastle, Co. Down (a designated bathing water), Omagh, Co. Tyrone (urban river system receiving agricultural inputs), and Craigavon, Co. Armagh (adjacent to Lough Neagh, a major recreational and drinking water source). Samples were filtered through 0.45µm cellulose-nitrate membranes and cultured on tryptone bile X-glucuronide agar with and without 4µg/mL cefotaxime (CTX) and CFU/100mL were determined. CTX-resistant E. coli isolates underwent antibiotic susceptibility testing (AST). DNA extracted from additional filters was used for microbial source tracking (MST) using human (HuBac) and ruminant (RuBac) markers.
E. coli concentrations positively correlated (<0.001) with rainfall 24h prior to sampling and temperature, indicating increased concentrations with wetter-warmer conditions. Similarly CTX-resistant E. coli concentrations also positively correlated (<0.001) with E. coli counts, rainfall and temperature and negatively with UV level. HuBac concentrations correlated with rainfall (<0.001), while RuBac correlated with rainfall and temperature (<0.001). Highest CTX-resistant E. coli concentrations were recorded in Newcastle (log10 2.2 CFU/100ml). AST revealed 52.6-100% resistance to ampicillin, amoxicillin-clavulanic acid, tetracycline, and norfloxacin with Newcastle and Omagh showing the greatest prevalence of multidrug resistance (MDR).
Our findings suggest that bathing waters can act as reservoirs for MDR bacteria, highlighting the need to incorporate AMR surveillance into water quality monitoring frameworks.