The impact of urban contamination on antibioresistance in microbial communities from periphyton and sediments

International audienceSince the early 20's antibiotics have been massively produced and consumed for the benefit of bothhuman and animal health. Nevertheless, antibiotics have also reached the aquatic environmentthrough diffuse sources (e.g. veterinary treatment, contaminated manure application...) and throughwastewater. Consequently, antibiotics concentrations between the ng/L and μg/L range are regularlydetected in surface water and those molecules have also been found in sediments and aquatic biota.The ubiquitous presence of antibiotics exerts a selective pressure on microbial communities leading tothe acquisition and dissemination of antibioresistance in the environment. While both antibiotics andantibioresistance have been found in different aquatic compartments, more investigation is requiredto better understand their distribution and to identify hot spots of accumulation.In this context, we investigated the repartition of antibiotics and antibioresistance in different aquaticcompartments on 4 stations belonging to regional observatories and presenting contrasting levels ofpharmaceuticals: 2 on the Arve river belonging to Sipibel observatory and 2 on Lake Geneva belongingto the Observatory on Lakes. On the Arve river, the 2 stations were located up- and down- stream thedischarge place of a wastewater treatment plant (WWTP) collecting both urban and hospitalwastewaters. On Lake Geneva, one station was located in a relatively pristine area while the secondwas close to the discharge of an urban WWTP. To better identify a potential temporal dynamic ofantibiotics and antibioresistances over seasons, 6 samplings were conducted during 1.5 year. On eachsampling campaign, the following parameters were determined: (i) antibiotics levels in water,sediments and periphyton; (ii) antibioresistance in periphyton and sediments using various techniques:detection of resistance genes, integrons quantification, detection of tolerance acquisition via a PICT(Pollution Induced Community Tolerance) approach; (iii) antibiotics biodegradation potential ofmicrobial community from sediments (by radiorespirometric measurement); (iv) diversity of bacteriaand diatoms in periphyton and sediments; (v) physico-chemical parameters and (vi) metalliccontamination in sediments.While microbial resistance to antibiotics is commonly assessed by quantifying resistance genes orisolating antibiotic resistant bacteria, antibiotic resistance can also be estimated by measuring theacquisition of antibiotics tolerance at community level, following a PICT approach. In our study,periphytic microbial communities from the Arve river were found to have a higher tolerance to thetested antibiotics (ciprofloxacin, ofloxacin, sulfamethazine and erythromycin) than communities fromLake Geneva, in agreement with the expected levels of contamination. In addition, in some cases, ahigher tolerance was also found at stations close to WWTP effluents than in upstream/protectedstations. For example, periphytic microbial communities collected downstream the WWTP on the Arveriver were generally found to have a higher tolerance to ciprofloxacin than the upstream communities.Comparing whole community tolerance to other classical indicators of antibioresistance and toantibiotics levels in the aquatic ecosystems allows us to better understand the interconnectionbetween pharmaceutical exposure, in situ tolerance and genetic potential for antibioresistance