Shallow groundwater exposure to antibiotic resistant Escherichia coli: hydrogeochemical approach to identify sources and transfer pathways
Résumé
Antimicrobial resistance is a growing public health concern in European hospitals and communities. Escherichia coli is one of the most common agents of bacterial infection which causes urinary tract infections as well as more serious infections. E. coli resistance to major antibiotics classes is increasing worldwide.
The aim of the project is to investigate the prevalence of extended-spectrum beta-lactamase (ESBL) producing E. coli in waste water treatment plants in the Burgundy region and to monitor the impact of treated effluents and sludge on water quality in the Ouche watershed near Dijon (East-central part of France). CTX-M is a recently occurring ESBL, encoded by the blaCTX-M genes, which causes resistance to 3rd generation cephalosporins (3GC).
A regional strategy for sampling surface and ground waters will be carried out in relation to existing data, in order to evaluate the capacity of CTX-M producing E. coli to spread and survive in water resources.
Based on previous data on E coli occurrences, we carried out sampling campaign through the studied watershed in order to evaluate the presence of E. coli and CTX-M producing E. coli in groundwater, surface water and springs. We also used molecular methods to monitor the presence of the blaCTX-M genes.
To characterize the dissemination of ESBL producing E. coli in the aquatic system, we have selected several sampling points according to hydrogeological contexts, land use and waste water plants with a particular interest for karst aquifers that are predominant in the studied area. Karst aquifers constitute an important volume of water resources but they are highly vulnerable to pollution even fecal coliform. In soils and aquifer, fecal coliforms are known to suffer retardation and degradation by sorption and filtering and die off. However, where by-pass occurs by preferential (fast) pathways (cracks, fissures and conduits) none of the retardation and degradation processes is effective.
For each sampling point, we combined microbial and chemical approaches.
Cultural detection of E. coli and ESBL producing E. coli was done by plating of selective TBX medium alone or supplemented with cefotaxime (3GC). Cefotaxim resistant isolates were then characterized by antibiotic susceptibility tests and MLST fingerprinting. blaCTX-M genes were monitored by real type PCR following DNA extraction.
Chemical analyses on inorganic elements (Major, trace elements) were performed to characterize the water composition as a tool to understand the water fluxes able to mobilize E. coli and identify the source of ESBL producing E. coli. Knowledge on water composition contributes to characterize hydrogeological features (rock type, time of contact…) mainly by understanding water-rock interactions of the studied system. Water composition allow to define chemical types of waters and anthropic pressure on water using chemical tracers such as agriculture pressure (NO3) or waste water (Boron). These classical parameters have been completed by analyses of REE among them Gadolinium. For tracing the different inputs of pharmaceutical products (that are related to antibiotic resistances) to groundwaters, several specific chemical markers are simultaneously monitored: Gadolinium, caffeine, carbamazepine, ibuprofen and acetaminophen. Positive Gd anomaly has been produced by the application of multidentate organic complexes of Gd in hospitals and clinics, as a contrast medium in magnetic resonance imaging (MRI) since 1988. From a hydro-geological point of view the anomalous Gd represents an excellent tool to trace the mixing of recycled water with surface and groundwater.
From the presence or absence of ESBL producing E. coli we attempt to identify the sources and vectors of water contamination by studying waste water treatment, land use (sewage sludge) and water fluxes in the studied watershed. The occurrence of CTX-M producing E. coli in groundwater resources and particularly the persistence of antibiotic resistance genes (ARG) such as blaCTX-M might constitute a health risk.