Abstract
Continuous exposure to low concentrations of antibiotics (sub-minimal inhibitory concentration: sub-MIC) is thought to lead to the development of antimicrobial resistance (AMR) in the environmental microbiota. However, the relationship between antibiotic exposure and resistance selection in environmental bacterial communities is still poorly understood and unproven. Therefore, we measured the concentration of twenty antibiotics, resistome quality, and analyzed the taxonomic composition of microorganisms in river biofilms collected upstream (UPS) and downstream (DWS) (at the point of discharge) from the wastewater treatment plant (WWTP) of Poitiers (France). The results of statistical analysis showed that the antibiotic content, resistome, and microbiome composition in biofilms collected UPS were statistically different from that collected DWS. According to Procrustes analysis, microbial community composition and antibiotics content may be determinants of antibiotic resistance genes (ARGs) composition in samples collected DWS. However, network analysis showed that the occurrence and concentration of antibiotics measured in biofilms did not correlate with the occurrence and abundance of antibiotic resistance genes and mobile genetic elements. In addition, network analysis suggested patterns of co-occurrence between several ARGs and three classes of bacteria/algae: Bacteroidetes incertae sedis, Cyanobacteria/Chloroplast, and Nitrospira, in biofilm collected UPS. The absence of a direct effect of antibiotics on the selection of resistance genes in the collected samples suggests that the emergence of antibiotic resistance is probably not only due to the presence of antibiotics but is a more complex process involving the cumulative effect of the interaction between the bacterial communities (biotic) and the abiotic matrix. Nevertheless, this study confirms that WWTP is an important reservoir of various ARGs, and additional efforts and legislation with clearly defined concentration limits for antibiotics and resistance determinants in WWTP effluents are needed to prevent their spread and persistence in the environment.
Highlights
Antibiotics (ATBs) are considered to be ubiquitous contaminants in all kinds of environmental matrices and present worldwide (Li et al, 2012; Gothwal and Shashidhar, 2015; Aus Der Beek et al, 2016; Patel et al, 2019)
These discharges lead to a constant presence of residual concentrations of ATBs and, exposure of naturally occurring aquatic bacteria that live in structured communities called biofilms (Besemer, 2016)
Statistical comparison of the values by Discriminant function analysis (DFA) showed that this difference is significant (Wilks’ lambda = 0.000002770 and p-value = 0.005—Table 1) between the biofilms collected from both sites
Summary
Antibiotics (ATBs) are considered to be ubiquitous contaminants in all kinds of environmental matrices (sediments, soils, water, plants and animals) and present worldwide (Li et al, 2012; Gothwal and Shashidhar, 2015; Aus Der Beek et al, 2016; Patel et al, 2019). Their main origin is related to their excretion and persistence in human or animal feces after administration. These discharges lead to a constant presence of residual concentrations of ATBs and, exposure of naturally occurring aquatic bacteria that live in structured communities called biofilms (Besemer, 2016)
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