Impacts of chemicals and microbiota from hospitals on the emergence of resistance in sewer systems

International audience

English. In the fight against the growing threat of antibiotic resistance, hospital wastewater is considered a hotspot, as it harbours a complex mixture of antibiotic-resistant bacteria, pathogenic bacteria and a cocktail of chemicals. The aim of this study was to clarify the respective roles of microbiota and chemicals from hospital wastewater in the emergence and dissemination of antibiotic resistance in mixed wastewater (hospital + domestic). As part of a field approach, domestic wastewater (DWW), hospital wastewater (HWW) and mixed wastewater were sampled and compared in terms of antibiotic concentrations, antibiotic resistance and taxonomic composition. In controlled microcosms, DWW was mixed with either full HWW, its chemical components alone, or its microbiota, and monitored for 96 hours. Antibiotic resistance was assessed by the percentage of bacteria resistant to ciprofloxacin and cefotaxime and the quantification of antibiotic resistance genes (ARGs). Multiplex sequencing of amplicons of ARG sequence variants from different classes and characterization of taxonomic composition were also used to study microbiota immigration. Finally, the SELECT method [1] was adapted in order to determine the lowest HWW proportion that significantly reduced the net growth of DWW microbiota. The percentage of bacteria resistant to ciprofloxacin was similar in the microcosms that received full HWW or only its chemical component, suggesting that selective pressure rather than community immigration was the main factor increasing antibiotic resistant bacteria. Indeed, the SELECT method showed a delay in the growth of DWW microbiota exposed to 20-fold diluted HWW chemicals, confirming their impact, even at really low concentrations. Moreover, the relative abundance of various genes was higher in microcosms exposed to HWW than the ones with DWW only. Certain ARG variants were specific to each type of wastewater. Their profiles in the microcosms suggest that hospital-derived variants can persist and coexist with domestic wastewater variants in some cases (blaMIR, mdtg...), while others were not maintained in the final microcosm communities (blaFOX, ermB). This research sheds light on the complex interplay between ARGs and chemical agents from hospitals in municipal wastewater, providing insights into the potential dissemination routes and persistence patterns.