The impact of urban contamination on antibioresistance in microbial communities from periphyton and sediments
Résumé
Since the early 20's antibiotics have been massively produced and consumed for the benefit of both
human and animal health. Nevertheless, antibiotics have also reached the aquatic environment
through diffuse sources (e.g. veterinary treatment, contaminated manure application...) and through
wastewater. Consequently, antibiotics concentrations between the ng/L and μg/L range are regularly
detected 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 to
the acquisition and dissemination of antibioresistance in the environment. While both antibiotics and
antibioresistance have been found in different aquatic compartments, more investigation is required
to better understand their distribution and to identify hot spots of accumulation.
In this context, we investigated the repartition of antibiotics and antibioresistance in different aquatic
compartments on 4 stations belonging to regional observatories and presenting contrasting levels of
pharmaceuticals: 2 on the Arve river belonging to Sipibel observatory and 2 on Lake Geneva belonging
to the Observatory on Lakes. On the Arve river, the 2 stations were located up- and down- stream the
discharge place of a wastewater treatment plant (WWTP) collecting both urban and hospital
wastewaters. On Lake Geneva, one station was located in a relatively pristine area while the second
was close to the discharge of an urban WWTP. To better identify a potential temporal dynamic of
antibiotics and antibioresistances over seasons, 6 samplings were conducted during 1.5 year. On each
sampling 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 of
microbial community from sediments (by radiorespirometric measurement); (iv) diversity of bacteria
and diatoms in periphyton and sediments; (v) physico-chemical parameters and (vi) metallic
contamination in sediments.
While microbial resistance to antibiotics is commonly assessed by quantifying resistance genes or
isolating antibiotic resistant bacteria, antibiotic resistance can also be estimated by measuring the
acquisition 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 the
tested antibiotics (ciprofloxacin, ofloxacin, sulfamethazine and erythromycin) than communities from
Lake Geneva, in agreement with the expected levels of contamination. In addition, in some cases, a
higher tolerance was also found at stations close to WWTP effluents than in upstream/protected
stations. For example, periphytic microbial communities collected downstream the WWTP on the Arve
river 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 to
antibiotics levels in the aquatic ecosystems allows us to better understand the interconnection
between pharmaceutical exposure, in situ tolerance and genetic potential for antibioresistance.
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