Tracking Cefotaxime-Resistant Escherichia coli and Vancomycin Resistant Enterococci hotspots in Newcastle, Northern Ireland

Antimicrobial resistance (AMR) is a global health concern. Surveillance of AMR bacteria has been well established in healthcare settings in Northern Ireland. However, investigations into the presence of AMR bacteria at designated bathing water sites is limited. Current legislation for monitoring water quality in bathing water does not require investigation of AMR bacteria. This is concerning as water is a medium transporting resistant bacteria and AMR genes and facilitates survival and proliferation of these organisms.
Newcastle, Co Down is a popular seaside town in Northern Ireland with a beach that is a designated bathing water site and, is frequently visited by people from throughout Northern Ireland and beyond. The beach receives the discharge from two rivers that flow through agricultural and urban areas.
In this study, we collected water samples from sites throughout the catchment from September to November 2024. Samples were filtered through cellulose nitrate filter membranes (0.45µm pore size) using an adapted method from ISO-7899-2 for the enumeration of intestinal enterococci and The Standing Committee of Analysts Method for enumeration of Escherichia coli. The membranes were placed on tryptone bile X-glucuronide (TBX) agar, TBX supplemented with cefotaxime (4µg/mL), Chromocult enterococci agar and Chromocult enterococci agar supplemented with vancomycin (8µg/mL). The plates were incubated for 24 hours and colonies were counted to calculate the CFU/100ml.
The study found a positive correlation between E. coli concentration and CTX-resistant E. coli, as well as enterococci concentration and vancomycin-resistant enterococci. Additionally, resistant enterococci was most frequently detected upstream of the urban area.