High concentration of ammonia sensitizes the response of microbial electrolysis cells to tetracycline

•High ammonia nitrogen reduced the tetracycline (TC) degradation capacity of MEC.•High ammonia nitrogen sensitized the response of anode respiring bacteria to TC.•TC and high ammonia nitrogen synergically reduced anode bio-activity and biomass.•The ARGs were closely related to microbial communities and MGE (intI1) in MEC.•The presence of MPs may lead to the risk of ARGs spreading to the environment.