Residual disinfectants in food-processing environments promote RP4 plasmid-mediated conjugative transfer through distinct donor and recipient responses

Antimicrobial resistance (AMR) is increasingly recognized as a critical threat to human health and food safety worldwide. Disinfectants are extensively used in food-processing environments for microbial control; however, their potential impact on the dissemination of AMR genes (ARGs) within the food chain remains unclear. Here, an Escherichia coli conjugation model harboring the broad-host-range plasmid RP4 was used to investigate the effects of sodium hypochlorite (NaClO) and benzalkonium bromide (BZK) on ARG dissemination and to elucidate the associated regulatory mechanisms. Both NaClO and BZK significantly enhanced RP4 plasmid transfer in a concentration- and time-dependent manner. BZK exhibited a more rapid and pronounced stimulatory effect, whereas NaClO induced a slower but more sustained response. Transmission electron microscopy, flow cytometry, RNA sequencing, and RT-qPCR revealed that both disinfectants induced intracellular oxidative stress and altered membrane integrity. NaClO primarily promoted plasmid dissemination through stimulating oxidative stress responses in donor cells and modulating gene expression associated with cell surface characteristics. By contrast, BZK rapidly triggered reactive oxygen species accumulation and activated the SOS response in recipient cells while simultaneously improving donor motility and recipient adhesion, thereby facilitating donor-recipient cell interactions. Furthermore, both disinfectants downregulated the expression of the RP4 regulatory elements korA, korB, and trbA, but upregulated conjugative transfer-related genes, including trbBp, traF, trfAp, and traJ. These findings elucidate the mechanisms through which commonly used disinfectants in food-processing environments may facilitate ARG dissemination and offer new insights for disinfectant risk assessment and the control of AMR transmission throughout the food supply chain.