AdeABC multidrug efflux pump is associated with decreased susceptibility to tigecycline in Acinetobacter calcoaceticus–Acinetobacter baumannii complex

Abstract

Objectives: To investigate the role of the AdeABC multidrug efflux pump in the decreased susceptibility of clinical isolates of Acinetobacter calcoaceticus-Acinetobacter baumannii complex to tigecycline.Methods: Gene expression was analysed by Taqman RT-PCR. A single cross-over achieved insertional inactivation of the adeB gene with a suicide plasmid construct carrying an adeB fragment obtained by PCR. Analysis of the adeRS locus was performed by PCR and sequencing. Ribotyping was performed with the RiboPrinter system. MICs were determined by Etest.Results: Expression analysis revealed constitutive overexpression of adeABC in less-susceptible clinical isolates G5139 and G5140 (tigecycline MIC 5 4 mg/L) when compared with the isogenic clinical isolates G4904 and G5141 (MIC 5 1.5 mg/L). Insertional mutants GC7945 (adeB knockout in G5139) and GC7951 (adeB knockout in G5140) were obtained, which resulted in tigecycline MICs of 0.5 mg/L. As reported previously, the expression of adeABC is regulated by the two-component signalling system encoded by the adeR and adeS genes. PCR and sequencing analyses revealed an insertion of an IS ABA-1 element in the adeS gene of G5139 and G5140. Conclusions:The results of this study suggest that decreased susceptibility to tigecycline in the A. calcoaceticus-A. baumannii complex is associated with the overexpression of the AdeABC multidrug efflux pump.

The role of the Serratia marcescens SdeAB multidrug efflux pump and TolC homologue in fluoroquinolone resistance studied via gene-knockout mutagenesis

“…This finding is consistent with Buckley et al (2006), where the authors reported a similar antibiotic-susceptibility trend for acrB and tolC knockouts in Salmonella enterica, and with Ruzin et al (2007), where the same finding was reported for an adeB knockout strain (inner-membrane transporter of the AdeABC multidrug efflux pump homologous to AcrAB of E. coli). Hypersusceptibility to a variety of compounds was also reported for acrAB deletion mutants in E. coli (Ma et al, 1995); AcrAB is a pump to which S. marcescens SdeAB is closely related.…”

Multidrug resistant Acinetobacter baumannii--the role of AdeABC (RND family) efflux pump in resistance to antibiotics.

“…This system was shown to be responsible for decreased susceptibility to a broad spectrum of antimicrobials. Aminoglicosides, tetracyclines, erythromycin, chloramphenicol, trimethoprim, fluoroquinolones, some β-lactams, ethidium bromide [30,37,73,135], and also recently tigecycline [92,110], were found to be substrates for AdeABC, although netilmicin and gentamicin appeared to be the best one for the pump [73].…”

“…Experiment performed by Ruzin et al [110] suggests, that AdeABC MDR efflux pump decreased susceptibility to tigecycline -the first member of a new class of modified tetracycline antimicrobials known as glycylcyclines. In this study the adeB gene was disrupted by insertional inactivation using a suicide plasmid in two derivative mutants constructed from two clinical isolates.…”

Genetic basis of antibiotic resistance in pathogenic Acinetobacter species

“…Tigecycline is the first commercially available member of the glycylcyclines, and multidrug-resistant strains of A. baumannii often retain susceptibility to tigecycline. Known mechanisms of resistance to tigecycline mainly involve active efflux by AdeABC, AdeIJK, and AdeFGH (35,44). Several worldwide reports indicate an increasing trend of resistance to tigecycline in isolates of A. baumannii (40).…”