Reactive oxygen species accelerate de novo acquisition of antibiotic resistance in E. coli

Reactive oxygen species (ROS) produced as a secondary effect of bactericidal antibiotics are hypothesized to play a role in killing bacteria. However, the role of ROS in the development of de novo resistance as a result of sublethal levels of bactericidal antibiotics has barely been investigated. Here, we report that single-gene knockout strains with reduced ROS scavenging exhibited enhanced ROS accumulation and more rapid acquisition of resistance when exposed to sublethal levels of bactericidal antibiotics. Consistent with this observation, the ROS scavenger thiourea in the medium decelerated resistance development. Thiourea downregulated the transcriptional level of error-prone DNA polymerase and DNA glycosylase MutM, which counters the incorporation and accumulation of 8-hydroxy-2-deoxyguanosine (8-HOdG) in the genome. The level of 8-HOdG significantly increased following incubation with bactericidal antibiotics but decreased after treatment with the ROS scavenger thiourea. These observations suggest that in E. coli sublethal levels of ROS stimulate de novo development of resistance, providing a mechanistic basis for hormetic responses induced by antibiotics. ImportanceExposure to sublethal concentrations of antimicrobials is known to result in de novo resistance development against the specific compound. Particularly, the use of antibiotics as feed additives to enhance productivity may result in the development of drug resistance in environmental and veterinary microorganisms, which could subsequently transfer to human populations. Nevertheless, the mechanisms underlying de novo resistance development have not been extensively explored. In this study, we indicate the role of ROS in promoting the formation of resistance to bactericidal antibiotics and show the potential of ROS scavengers to reduce mutation rates and slow down resistance formation under long-term selection. Thus, the supplementary use of antioxidants during prolonged antibiotic administration potentially contributes to mitigating the emergence of antimicrobial resistance.