Contributions of RecA and RecBCD DNA repair pathways to the oxidative stress response and sensitivity of Acinetobacter baumannii to antibiotics

Abstract

ObjectivesRecA and RecBCD are responsible for the repair of oxidative DNA damage in bacteria, including Acinetobacter baumannii (A. baumannii). This study evaluated the contribution of recA, recB, recC and recD to the sensitivity and oxidative response of A. baumannii to antibiotics. ResultsInactivation of recA, recB, recC and recD significantly increased the susceptibility of A. baumannii AB5075 to colistin, gentamicin, rifampicin and tigecycline. Furthermore, superoxide anion radicals (•O2−) and hydrogen peroxide (H2O2) accumulated in colistin, gentamicin, rifampicin or tigecycline-treated ΔrecA, ΔrecB, ΔrecC and ΔrecD mutants compared with the parental strain. Concomitantly, a more pronounced increase in fragmented DNA was observed in the mutants compared with the parental strain upon antibiotic treatment. Chelation of ferrous ion (Fe2+) with dipyridyl lowered the susceptibility of ΔrecA, ΔrecB, ΔrecC and ΔrecD strains of A. baumannii to colistin, gentamicin and rifampicin, but not tigecycline, to a level comparable with the parental strain. Antibiotic-mediated accumulation of reactive oxygen species depleted glutathione, with a more profound response in the mutants compared with the parental strain. The antibiotics, except tigecycline, raised the oxidized nicotinamide adenine dinucleotide/reduced nicotinamide adenine dinucleotide and adenosine diphosphate/adenosine triphosphate ratio of ΔrecA, ΔrecB, ΔrecC and ΔrecD mutants compared with the parental strain. ConclusionReduced capability of ΔrecA, ΔrecB, ΔrecC and ΔrecD mutants to repair DNA raised the susceptibility of A. baumannii to colistin, gentamicin, rifampicin and tigecycline. The available data further support the notion that oxidative stress contributes to antibiotic-mediated bacterial killing.