Ter Kuile, B. H. | bioRxiv Science

bioRxiv2024

Fluoroquinolone-Specific Resistance Trajectories in E. coli and their Dependence on the SOS-Response

Fluoroquinolones are essential for treating bacterial infections in both human and veterinary medicine. This study investigates the mechanisms behind acquired resistance to fluoroquinolones with a specific focus on the SOS response - a critical cellular pathway activated by DNA damage. Utilizing an experimental evolution approach, we exposed Escherichia coli to four fluoroquinolones and monitored the adaptation process. A recA knock-out mutant deficient in the SOS response was used as biological control. The emergence of resistance was accompanied by numerous DNA mutations, consisting of some observed often and others that infrequently appeared. Our findings indicate that the development of resistance depends in varying degrees on the SOS response among the tested fluoroquinolones, with notable dissimilarities in clinical resistance development. Resistance developed slowest to ciprofloxacin, then levofloxacin, followed by enrofloxacin, and fastest to moxifloxacin. Genomic analysis revealed distinct mutation profiles in cultures exposed to the tested antimicrobials, emphasizing the unique adaptation strategies of bacteria. This research underscores the importance of recognizing the differences among fluoroquinolones in scientific research and clinical practice.

microbiology↗

bioRxiv2023

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.

microbiology↗