Effect of sulfamethazine on the horizontal transfer of plasmid-mediated antibiotic resistance genes and its mechanism of action

•SM2 (10 and 100 mg/L) enhanced the conjugative transfer of ARGs between E. coli.•SM2 (>10 mg/L) increased the permeability of the cell membrane.•SM2 could affect the activities or content of antioxidants in bacteria.•SM2 affected the transfer of ARGs by regulating cell membrane and gene expression.