Insight into the spread potential of antibiotic resistance genes during aerobic biofilm treatment of ofloxacin-containing rural domestic sewage

Controlling antibiotic resistance genes (ARGs) requires understanding their dissemination potential during treatment of antibiotic-laden rural sewage. However, the mechanisms of ARG spread during aerobic biofilm treatment of antibiotic-containing rural domestic sewage remain unclear. Here, we constructed the aerobic biofilm systems to examine the ARG spread in response to ofloxacin (OFL) with increasing exposure concentrations during rural domestic sewage treatment. Metagenomic analysis revealed that after 35 days of exposure, 0.1, 1, and 10 mg/L OFL increased total ARG abundance by 7.32 %, 10.82 %, and 16.37 %, respectively, compared to the control group. Potential ARG host analysis revealed that OFL stimulates the acquisition of ARGs by pathogens with Acinetobacter baumannii and Escherichia coli being the main pathogenic-resistant bacteria. Network analysis indicated that host bacteria potentially acquire ARGs through horizontal gene transfer (HGT) in OFL-stressed aerobic biofilm systems. Functional analysis showed that SOS response, high cell membrane permeability, adenosine triphosphate synthesis, extracellular polymeric substances secretion, and the enrichment of mobile genetic elements (MGEs) were triggered by OFL, which subsequently promoted the HGT of ARGs. Partial least-squares path modeling suggested MGEs might be primarily driven by ARG spread under OFL exposure in aerobic biofilm systems. These findings provide advanced insights into the unique role of OFL to the host and the HGT of ARGs during aerobic biofilm systems treatment of rural domestic sewage.