Investigations of associations between catchment-scale processes and the abundance of Escherichia coli in bathing waters that are phenotypically resistant to clinically important antibiotics.

Abstract

The environment is important in terms of antimicrobial resistance emergence and spread. This study is the first to look at how antimicrobial resistance could be monitored at bathing water sites, develop models for different catchment processes impacting on antimicrobial resistant E. coli and estimate UK bather exposure. Methods: 332 water samples were collected at 10 bathing waters during the 2019 and 2021 bathing seasons. Standard methods for microbiological bathing water analysis were adapted to enumerate E. coli phenotypically resistant to clinically important antibiotics: ampicillin, cefotaxime, amikacin, and meropenem. Catchment-level data were obtained to explore associations between landscape-scale processes and resistant E. coli abundance at coastal bathing water sites. Cefotaxime-resistant E. coli isolates were characterised using PCR and WGS to investigate trends in catchment use and features of resistant E. coli. Additionally, human exposure to resistant E. coli was estimated. Results: E. coli resistant to ampicillin and cefotaxime were commonly isolated, whilst resistance to amikacin and meropenem were rare. Human-associated factors increased the abundance of ampicillin-resistant E. coli in bathing water catchments as a whole, although these trends were not observed in every individual catchment. Exposure estimates indicated large-scale bather exposure to antibiotic-resistant bacteria, with ampicillin-resistant E. coli estimated to be 37.3 million bathing sessions, and cefotaximeresistant E. coli 11.7 million sessions. Characterisation showed that exposure to cefotaxime resistant E. coli belonging to pathogen-associated phylogroups was estimated to be 7.8 million sessions in England and predicted to be greater in urban catchments as prevalence of pathogenic E. coli was statistically higher than in rural catchments. Conclusions: Bathers in the UK are exposed to E. coli that are phenotypically resistant to clinically important antibiotics in coastal bathing waters. Since 2012, the prevalence of cefotaxime resistant E. coli in bathing waters has increased by approximately 6.5 times. Exposure estimates highlight the potential risk to human health of antimicrobial resistant bacteria in bathing waters, particularly resistant pathogens, underpinning the need for antimicrobial resistance surveillance in bathing waters and the wider environment. Human associated factors were associated with higher abundance of resistant E. coli. Based on the results of this study, and the literature, recommendations are put forward that will aid the design of a national AMR surveillance programme in bathing waters.