Acinetobacter baumannii RecA Protein in Repair of DNA Damage, Antimicrobial Resistance, General Stress Response, and Virulence

Abstract

RecA is the major enzyme involved in homologous recombination and plays a central role in SOS mutagenesis. In Acinetobacter spp., including Acinetobacter baumannii, a multidrug-resistant bacterium responsible for nosocomial infections worldwide, DNA repair responses differ in many ways from those of other bacterial species. In this work, the function of A. baumannii RecA was examined by constructing a recA mutant. Alteration of this single gene had a pleiotropic effect, showing the involvement of RecA in DNA damage repair and consequently in cellular protection against stresses induced by DNA damaging agents, several classes of antibiotics, and oxidative agents. In addition, the absence of RecA decreased survival in response to both heat shock and desiccation. Virulence assays in vitro (with macrophages) and in vivo (using a mouse model) similarly implicated RecA in the pathogenicity of A. baumannii. Thus, the data strongly suggest a protective role for RecA in the bacterium and indicate that inactivation of the protein can contribute to a combined therapeutic approach to controlling A. baumannii infections.

Antibiotic Resistance Acquired through a DNA Damage-Inducible Response in Acinetobacter baumannii

“…We simulated desiccation-induced DNA damage by drying A. baumannii cells on filters for a period of time, resulting in standardized killing (see Materials and Methods). As expected and in agreement with previous findings (30), recA::Km cultures were more sensitive to drying than the parental cultures (data not shown). Cells were rehydrated and grown in rich liquid medium to assess the frequency of Rif r mutants.…”

“…It is known that A. baumannii is able to survive on hospital equipment for long periods of time and has considerable desiccation tolerance (3,4). Desiccation and desiccation-rehydration cause various DNA lesions, including alkylation, oxidation, cross-linking, base removal, and strand breaks (66); and it has been reported that A. baumannii ATCC 17978 recA::Km cells are sensitive to desiccation stress (30). It is likely that A. baumannii cells on the surfaces of hospital equipment incur these types of desiccation-induced DNA lesions.…”

“…The dinB::Km insertion knockout was created using a method developed by Aranda et al (30) with some modifications. An amplicon of approximately 3,000 bp was constructed by splicing by overlap extension PCR (51).…”

“…RecA is also necessary for homologous recombination (26) and participates in the DNA damage tolerance pathway by forming complexes with translesion synthesis (TLS) DNA polymerases DinB (or DNA polymerase IV [Pol IV] [27]) and DNA Pol V (27)(28)(29). A. baumannii encodes a predicted recA gene that when knocked out sensitizes it to DNA damage and a number of different stressors (30). Moreover, recA and ddrR (encoding a protein of unknown function) are induced upon UV irradiation in Acinetobacter baylyi ADP1 (31,32), a nonpathogenic strain of Acinetobacter, suggesting a key role for RecA in mechanisms involved in stress survival.…”

Recent Advances in the Immunopathogenesis of Acinetobacter baumannii Infection

“…Another bacterial enzyme that was recently shown to play a role in virulence is recA (50). This protein was found not only to mediate DNA repair in A. baumannii but also played a role in desiccation resistance, prevented killing inside macrophages as well as contributed to mouse lethality.…”