Sewers as potential reservoirs of antibiotic resistance

Este artículo contiene 8 páginas, 4 figuras, 1 tabla.Wastewater transport along sewers favors the colonization of inner pipe surfaces by wastewater-derived microorganisms that grow forming biofilms. These biofilms are composed of rich and diverse microbial communities that are continuously exposed to antibiotic residues and antibiotic resistant bacteria (ARB) from urban wastewater. Sewer biofilms thus appear as an optimal habitat for the dispersal and accumulation of antibiotic resistance genes (ARGs). In this study, the concentration of antibiotics, integron (intI1) and antibiotic resistance genes (qnrS, sul1, sul2, blaTEM, blaKPC, ermB, tetM and tetW), and potential bacterial pathogens were analyzed in wastewater and biofilm samples collected at the inlet and outlet sections of a pressurized sewer pipe. The most abundant ARGs detected in both wastewater and biofilm samples were sul1 and sul2 with roughly 1 resistance gene for each 10 copies of 16s RNA gene. Significant differences in the relative abundance of gene intI1 and genes conferring resistance to fluoroquinolones (qnrS), sulfonamides (sul1 and sul2) and betalactams (blaTEM) were only measured between inlet and outlet biofilm samples. Composition of bacterial communities also showed spatial differences in biofilms and a higher prevalence of Operational Taxonomic Units (OTUs) with high sequence identity (N98%) to wellknown human pathogens was observed in biofilms collected at the inlet pipe section. Our study highlights the role of sewer biofilms as source and sink of ARB and ARGs and supports the idea that community composition rather than antibiotic concentration is the main factor driving the diversity of the sewage resistome.The authors would like to acknowledge the Consorci Costa Brava, Empresa Mixta Aigües Costa Brava for their help in the sampling campaigns, the projects of SEWAGENE CTM2016-75653-R and REaCH CTM2015-66892-R funded by the Spanish Government. This work has been co-financed by the European Union through the European Regional Development Fund (ERDF) and supported by the Generalitat de Catalunya (Consolidated Research Group: Catalan Institute for Water Research 2014 SGR 291). S. Rodriguez-Mozaz acknowledges the Ramon y Cajal program (RYC-2014-16707). XT was supported by project BRIDGES CGL2015-69043-P from the Spanish Office for Research MINECO.Peer reviewe