RESUMEN
Sewer biofilms are likely to constitute hotspots for selecting and accumulating antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). This study aimed to optimize culture conditions to obtain in vitro biofilms, mimicking the biofilm collected in sewers, to study the impact of fluoroquinolones (FQs) on sewer biofilm microbiota. Biofilms were grown on coupons in CDC Biofilm Reactors®, continuously fed with nutrients and inoculum (1/100 diluted wastewater). Different culture conditions were tested: (i) initial inoculum: diluted wastewater with or without sewer biofilm, (ii) coupon material: concrete vs. polycarbonate, and (iii) time of culture: 7 versus 14 days. This study found that the biomass was highest when in vitro biofilms were formed on concrete coupons. The biofilm taxonomic diversity was not affected by adding sewer biofilm to the initial inoculum nor by the coupon material. Pseudomonadales, Burkholderiales and Enterobacterales dominated in the sewer biofilm composition, whereas in vitro biofilms were mainly composed of Enterobacterales. The relative abundance of qnrA, B, D and S genes was higher in in vitro biofilms than sewer biofilm. The resistome of sewer biofilm showed the highest Shannon diversity index compared to wastewater and in vitro biofilms. A PCoA analysis showed differentiation of samples according to the nature of the sample, and a Procrustes analysis showed that the ARG changes observed were linked to changes in the microbial community. The following growing conditions were selected for in vitro biofilms: concrete coupons, initial inoculation with sewer biofilm, and a culture duration of 14 days. Then, biofilms were established under high and low concentrations of FQs to validate our in vitro biofilm model. Fluoroquinolone exposure had no significant impact on the abundance of qnr genes, but high concentration exposure increased the proportion of mutations in gyrA (codons S83L and D87N) and parC (codon S80I). In conclusion, this study allowed the determination of the culture conditions to develop an in vitro model of sewer biofilm; and was successfully used to investigate the impact of FQs on sewer microbiota. In the future, this setup could be used to clarify the role of sewer biofilms in disseminating resistance to FQs in the environment.
RESUMEN
Antibiotic resistance (AR) is one of the major health threats of our time. The presence of antibiotics in the environment and their continuous release from sewage treatment plants, chemical manufacturing plants and animal husbandry, agriculture and aquaculture, result in constant selection pressure on microbial organisms. This presence leads to the emergence, mobilization, horizontal gene transfer and a selection of antibiotic resistance genes, resistant bacteria and mobile genetic elements. Under these circumstances, aquatic wildlife is impacted in all compartments, including freshwater organisms with partially impermeable microbiota. In this narrative review, recent advancements in terms of occurrence of antibiotics and antibiotic resistance genes in sewage treatment plant effluents source compared to freshwater have been examined, occurrence of antibiotic resistance in wildlife, as well as experiments on antibiotic exposure. Based on this current state of knowledge, we propose the hypothesis that freshwater aquatic wildlife may play a crucial role in the dissemination of antibiotic resistance within the environment. Specifically, we suggest that organisms with high bacterial density tissues, which are partially isolated from the external environment, such as fishes and amphibians, could potentially be reservoirs and amplifiers of antibiotic resistance in the environment, potentially favoring the increase of the abundance of antibiotic resistance genes and resistant bacteria. Potential avenues for further research (trophic transfer, innovative exposure experiment) and action (biodiversity eco-engineering) are finally proposed.
