Preservatives accelerate the horizontal transfer of plasmid-mediated antimicrobial resistance genes via differential mechanisms

Increasing concentrations of preservatives have been detected in environments due to the overuse and misuse of preservatives in food and personal care products. Recent studies have relied heavily on the toxicity, biodegradability, and fate of preservatives in the environment. However, the biological effects of preservatives on antimicrobial resistance, which poses great threats to public health worldwide, are largely unknown. This study investigated three preservatives for their ability and mechanisms of promoting horizontal transfer of antimicrobial resistance genes (ARGs). The results demonstrated that these preservatives (sodium nitrite, sodium benzoate, and triclocarbon), under daily-use concentrations, led to concentration-dependent increases in conjugative transfer by 1.24-2.63, 6.79-7.05, and 2.17-4.31 folds compared with the control group. Even these three preservatives had different patterns on generating intracellular reactive oxidative species (ROS) and reactive nitrogen species (RNS), all of them could stimulate radical-induced RpoS regulon and SOS response, increase cell membrane permeability, and regulate conjugative transfer-related genes, subsequently promoting horizontal transfer of ARGs. The present results expanded the understanding of biological effects induced by preservatives, and provided mechanistic insight into the preservatives-induced resistance. This study also opens an intriguing question on the roles of emerging contaminants including preservatives in the emerging and spread of ARGs in various environments.