A Sublethal Concentration of Chlorine Induces Antibiotic Resistance in Salmonella via Production of Reactive Oxygen Species

Studies have shown that the production of reactive oxygen species (ROS) is triggered by bactericidal antibiotics, which contributes significantly to the killing of bacterial cells and increasing mutations in surviving cells. In this study, we hypothesized that exposure of Salmonella to sublethal concentrations of hypochlorite (NaOCl), a commonly used sanitizer in household and food industries increases mutation rates, leading to the development of antibiotic resistance. We found that a sublethal concentration (20 ppm) of NaOCl increased the mutation rates of S. typhimurium 14028s significantly (p < 0.05), which was prevented by the ROS scavenger thiourea, supporting that the increased mutation was due to NaOCl-triggered ROS production. We further found that the exposure of S. typhimurium 14028s to the same sublethal concentration of NaOCl increases resistance to kanamycin among the 3 antibiotics evaluated. The results of this study suggest that when NaOCl applied as a sanitizer fails to kill Salmonella due to diluted local concentrations or presence of organic materials, it can cause an adverse outcome of developing antibiotic resistance of the pathogen.