Résumé
Waters play a crucial role in interconnecting different ecosystems like humans, animals, soils and hydrosystems, contributing to the circulation of antibiotic-resistant bacteria. Karstic hydrosystems are commonly known to be vulnerable to anthropogenic contaminations due to direct connections between surface water and groundwater and to be heterogeneous due to the contrast between waters stored in some compartments (with long residence time) and waters with fast transit. Considered as integrator ecosystems, natural waters are of great interest to survey the antibiotic resistance in the environment, which is relevant to human health. Among natural hydrosystems, karstic aquifers are poorly investigated for emergence and dissemination of antibioresistance. The question of their role as reservoir for antimicrobial resistance according their hydrogeological characteristics remains open.The Lez karst hydrosystem supplies drinking water to the metropolitan region of Montpellier, in southern France. The aim of this study is to evaluate the resistance level and the biodiversity of bacterial communities in the Lez aquifers in contrasted hydrogeological conditions and seasonality. For this purpose, we develop an original mixed method associating i) selective culture, using culture media containing tetracycline,vancomycin, ofloxacin, amoxicillin, cefotaxime or ceftazidime at increasing concentrations, and ii) molecular approaches, implementing 16S rRNA gene PCR-Temporal Temperature Gradient Gel Electrophoresis (TTGE) and sequencing. Minimal antibiotic concentrations inhibiting 50%, 70% and 90% of the whole culturable community were determined. Resistance to beta-lactams were clearly fluctuant between both compartments and periods of sampling, whereas differences obtained with the others antibiotics were not so marked. Then, the taxonomic diversity and the dynamics of the resistant sub-communities were described.These results show that hydrogeological conditions and thus the speed of water circulation in the karst aquifer can impact the resistance of bacterial communities. Then, the potential risk of bacterial resistance will be discussed in term of resistance transferability and relevance in clinical epidemiology.