Private and well drinking water are reservoirs for antimicrobial resistant bacteria

Abstract

Water quality testing does not recognise antimicrobial resistance (AMR) and is often limited to indicators of faecal contamination Escherichia coli and Enterococcus species. In Europe, data on AMR in drinking water is scarce. In Ireland, as in many countries, household drinking water is supplied via mains or via private wells or water schemes. Using citizen science, we identified Irish private drinking water supplies as reservoirs of antimicrobial resistant bacteria (ARB). Gram-negative (n = 464) and Gram-positive (n = 72) bacteria were isolated. We identified instances of potentially opportunistic ARB such as Enterobacter cloacae, Acinetobacter baumannii and Enterococcus species. We report reservoirs of multidrug resistance in Enterococcus casseliflavus, E. cloacae, E. coli, Stenotrophomonas maltophilia, and Serratia rubidaea. We also identified linezolid-resistant Enterococcus in Irish drinking water. Linezolid is a last-resort antibiotic used to treat vancomycin-resistant Enterococcus sp. Additionally, we identified mobile AMR in three water samples, two of which were carried on IncF group, one on IncQ and five on Col-like plasmids. Our work suggests that private drinking water is a potential sink and source of AMR pathogens. This highlights a value of drinking water surveillance in a One Health framework as the surveillance would provide information regarding the movement and persistence of ARB and ARGs that are able to survive in drinking water and subsequently have the opportunity to be mobilised through humans; linking the environment to the human and potentially threatening human health.

Fig. 1. Flow chart summary of key outputs of sampling and analysis.

Household and Group Water Scheme numbers are confidential identifiers. The households are classified based on private ownership of the water supply or dependence on Group Water Schemes (S1–S6). The geographical breakdown of households is focused on the East & Midlands, the West or Northern Ireland. For each region, the number of households harbouring viable bacteria is indicated. These bacteria are grouped based on phenotype (AMR or MDR). The households and species which harboured MDR isolates are shown. GWS: Group Water Scheme, AMR: Antimicrobial-Resistant, MDR: Multidrug-Resistant.

Fig. 2. AMR species of clinical relevance identified in private drinking water.

The bar chart shows the different species of clinical relevance and the numbers which were identified as being antimicrobial resistant. The blue denotes the total number of isolates from each species of relevance, red signifies the number of isolates identified as resistant to at least one class of antimicrobial and yellow indicates resistance to at minimum one class of antimicrobials. MDR: Multidrug-Resistant.

Fig. 3. Resistance patterns of antimicrobial resistant bacteria isolated from drinking water belonging to household 36.

The resistance patterns for multidrug-resistant (a) Escherichia coli and (b) antimicrobial resistant Serratia rubideae shows similarity in resistance patterns against phenicols, aminoglycosides and tetracycline. Blue represents susceptibility, yellow signifies intermediate resistance and red denotes resistance of the isolate to the antimicrobial. The numbers assigned are arbitrary identifiers. AK amikacin, AMP ampicillin, C chloramphenicol, CN gentamicin, COL colistin, CTX cefotaxime, K kanamycin, TET tetracycline, CAZ ceftazidime, CIP ciprofloxacin, IMP imipenem, W trimethoprim.

Fig. 4. Antimicrobial susceptibility patterns of transconjugants.

The resistance patterns of E. coli transconjugants from Households 36, 14 and 43 are shown where blue represents susceptibility, yellow signifies intermediate resistance and red denotes resistance of the transconjugant to the antimicrobial. The numbers assigned to each transconjugant are arbitrary identifiers. Letters next to the numbers represent the antimicrobial used to select the transconjugants: tetracycline (t), ciprofloxacin (c), amoxicillin (a). AMP ampicillin, TET tetracycline, CIP ciprofloxacin, C chloramphenicol, AK amikacin.