Synergistic Effect of SOS Response and GATC Methylome Suppression on Antibiotic Stress Survival in Escherichia coli

The suppression of the SOS response has been shown to enhance the activity of quinolones. Furthermore, Dam-dependent base methylation has an impact on susceptibility to other antimicrobials affecting DNA synthesis. Here, we investigated the interplay between these two processes, alone and in combination, in terms of antimicrobial activity. A genetic strategy was used employing single- and double-gene mutants for the SOS response ( gene) and the Dam methylation system ( gene) in isogenic models of Escherichia coli both susceptible and resistant to quinolones. Regarding the bacteriostatic activity of quinolones, a synergistic sensitization effect was observed when the Dam methylation system and the gene were suppressed. In terms of growth, after 24 h in the presence of quinolones, the Δ Δ double mutant showed no growth or delayed growth compared to the control strain. In bactericidal terms, spot tests showed that the Δ Δ double mutant was more sensitive than the Δ single mutant (about 10- to 10 -fold) and the wild type (about 10 - to 10 -fold) in both susceptible and resistant genetic backgrounds. Differences between the wild type and the Δ Δ double mutant were confirmed by time-kill assays. The suppression of both systems, in a strain with chromosomal mechanisms of quinolone resistance, prevents the evolution of resistance. This genetic and microbiological approach demonstrated the enhanced sensitization of E. coli to quinolones by dual targeting of the (SOS response) and Dam methylation system genes, even in a resistant strain model.