Groundwater as a source and pathway for antibiotic-resistant infection in the Republic of Ireland

Antibiotic resistant organisms and genes are now acknowledged as significant emerging aquatic contaminants with potentially adverse human health impacts. The current study is an environmental health investigation on the... [ view full abstract ]

Antibiotic resistant organisms and genes are now acknowledged as significant emerging aquatic contaminants with potentially adverse human health impacts. The current study is an environmental health investigation on the presence of antimicrobial-resistant (AR) bacteria (E. coli) in Irish groundwater, and the role of anthropogenic and natural drivers on levels of resistance.  Antibiotic susceptibility testing was carried out on groundwater-derived E. coli isolates (N = 125) against a panel of commonly prescribed human (N = 13) and veterinary (N = 8) therapeutic antibiotics. Geo-spatial data extraction and geo-statistical analyses were employed to elucidate the sources and transport mechanisms associated with antimicrobial presence in groundwater. Resistance to the human panel of antibiotics was moderate (21.4%) with the most frequently occurring resistance phenotypes associated with 1^st/2nd generation broad spectrum antimicrobials. Highest levels of resistance were associated with the penicillins, while notable levels of resistance were found among the fluoroquinolones. In contrast, high levels of resistance to veterinary antibiotics were found; all isolates presented resistance to >1 veterinary antibiotic, with high levels of resistance (93%) found among the aminoglycosides. Geostatistical modelling indicates a significant association between the presence of both human AR (p =0.011) and Multiple Antibiotic Resistance (MAR) (p =0.002) and Domestic Waste Water Treatment Systems (DWWTS) reliance, indicating that regions characterised by a higher density of septic tanks are associated with the presence of AR E. coli. Furthermore, a significant association was found between households comprising children <5 years and the presence of both human AR (p = 0.022) and MAR (p <0.001). Results also indicate a significant relationship (p = <0.001) between livestock density and the prevalence of veterinary MAR. This study presents evidence of the presence and extent of AR in E.coli isolates the Irish groundwater environment, which represents the primary daily source of drinking water for ≈750,000 people.