Contribution of Efflux Pumps, Porins, and β-Lactamases to Multidrug Resistance in Clinical Isolates of Acinetobacter baumannii

Abstract

eWe investigated the mechanisms of resistance to carbapenems, aminoglycosides, glycylcyclines, tetracyclines, and quinolones in 90 multiresistant clinical strains of Acinetobacter baumannii isolated from two genetically unrelated A. baumannii clones: clone PFGE-ROC-1 (53 strains producing the OXA-58 ␤-lactamase enzyme and 18 strains with the OXA-24 ␤-lactamase) and clone PFGE-HUI-1 (19 strains susceptible to carbapenems). We used real-time reverse transcriptase PCR to correlate antimicrobial resistance (MICs) with expression of genes encoding chromosomal ␤-lactamases (AmpC and OXA-51), porins (OmpA, CarO, Omp33, Dcap-like, OprB, Omp25, OprC, OprD, and OmpW), and proteins integral to six efflux systems (AdeABC, AdeIJK, AdeFGH, CraA, AbeM, and AmvA). Overexpression of the AdeABC system (level of expression relative to that by A. baumannii ATCC 17978, 30-to 45-fold) was significantly associated with resistance to tigecycline, minocycline, and gentamicin and other biological functions. However, hyperexpression of the AdeIJK efflux pump (level of expression relative to that by A. baumannii ATCC 17978, 8-to 10-fold) was significantly associated only with resistance to tigecycline and minocycline (to which the TetB efflux system also contributed). TetB and TetA(39) efflux pumps were detected in clinical strains and were associated with resistance to tetracyclines and doxycycline. The absence of the AdeABC system and the lack of expression of other mechanisms suggest that tigecycline-resistant strains of the PFGE-HUI-1 clone may be associated with a novel resistance-nodulation-cell efflux pump (decreased MICs in the presence of the inhibitor Phe-Arg ␤-naphthylamide dihydrochloride) and the TetA(39) system.

Determination of Different Fluoroquinolone Mechanisms Among Clinical Isolates of Acinetobacter baumannii in Tehran, Iran

“…Resistance to quinolones is developed through different methods, one of which is the changes occurred in the expression of the efflux pumps. The efflux pump in A. baumannii is the AdeABC pump and is of great importance in terms of resistance creation (10). One of the mechanisms to deal with the antibiotic resistance is to block or disrupt the mechanisms leading to resistance.…”

Identification of Acinetobacter baumannii Serum-Associated Antibiotic Efflux Pump Inhibitors

“…With regard to the efflux pumps, the organism has been shown to harbor representatives of each of the five so-called bacterial drug efflux pump families: CraA and AmvA are major facilitator superfamily (MFS) pumps that are proposed to efflux chloramphenicol and erythromycin, respectively (13,14), AbeM is a multidrug and toxic compound extrusion (MATE) family protein that effluxes aminoglycosides, quinolones, and chloramphenicol (15), AbeS is a small multidrug resistance (SMR) family pump that confers resistance to erythromycin and novobiocin, as well as low-level tolerance to aminoglycosides, quinolones, tetracycline, and trimethoprim (16), AdeABC, AdeFGH, and AdeIJK are resistance-nodulation-division (RND) family pumps that have been associated with resistance to aminoglycosides, ␤-lactams, fluoroquinolones, tetracyclines, tigecycline, macrolides, chloramphenicol, and trimethoprim (17)(18)(19)(20)(21). Furthermore, A. baumannii is known to harbor several horizontally acquired Tet efflux pumps belonging to the MFS that confer tetracycline resistance (12,22). While the antimicrobial effects of these efflux pumps have been well documented, the mechanisms by which the organism regulates their expression are only beginning to be understood.…”

“…baumannii antibiotic resistance is thought to be mediated by an expansive repertoire of enzymatic determinants, such as ␤-lactamases, as well as efflux pumps that extrude toxic agents, including antibiotics, from the cell (3,11,12). With regard to the efflux pumps, the organism has been shown to harbor representatives of each of the five so-called bacterial drug efflux pump families: CraA and AmvA are major facilitator superfamily (MFS) pumps that are proposed to efflux chloramphenicol and erythromycin, respectively (13,14), AbeM is a multidrug and toxic compound extrusion (MATE) family protein that effluxes aminoglycosides, quinolones, and chloramphenicol (15), AbeS is a small multidrug resistance (SMR) family pump that confers resistance to erythromycin and novobiocin, as well as low-level tolerance to aminoglycosides, quinolones, tetracycline, and trimethoprim (16), AdeABC, AdeFGH, and AdeIJK are resistance-nodulation-division (RND) family pumps that have been associated with resistance to aminoglycosides, ␤-lactams, fluoroquinolones, tetracyclines, tigecycline, macrolides, chloramphenicol, and trimethoprim (17)(18)(19)(20)(21).…”

Assessment of Efflux Activity Using H33342 Accumulation in Tigecycline-ResistantAcinetobacter baumanniiClinical Isolates

“…The AdeABC pump is present in approximately 80% (53% to 97%) of A. baumannii clinical strains [2,14]. Our study showed the presence of the adeB gene in all 120 A. baumannii clinical isolates.…”