Wastewater pollution differently affects the antibiotic resistance gene pool and biofilm bacterial communities across streambed compartments

Wastewater discharges introduce antibiotic residues and antibiotic-resistant bacteria (ARB) into surface waters. Both inputs directly affect the streambed resistome, either by exerting a selective pressure that favor the proliferation of resistant phenotypes or by enriching the resident communities with wastewater-associated ARB. Here, we investigated the impact of raw and treated urban wastewater discharges on epilithic (growing on rocks) and epipsammic (growing on sandy substrata) streambed biofilms. The effects were assessed by comparing control and impact sites i) on the composition of bacterial communities; ii) on the abundance of twelve antibiotic resistance genes (ARGs) encoding resistance to β-lactams, fluoroquinolones, sulfonamides, tetracyclines, macrolides and vancomycin, as well as the class 1 integron-integrase gene (intI1); and iii) on the occurrence of wastewater-associated bacteria, including putative pathogens, and their potential linkage to target ARGs. We measured mor...