Abstract
BackgroundMulti-drug efflux pumps have been increasingly recognized as a major component of resistance in P. aeruginosa. We have investigated the expression level of efflux systems among clinical isolates of P. aeruginosa, regardless of their antimicrobial susceptibility profile.ResultsAztreonam exhibited the highest in vitro activity against the P. aeruginosa isolates studied (64.4% susceptibility), whereas susceptibility rates of imipenem and meropenem were both 47.5%. The MexXY-OprM and MexAB-OprM efflux systems were overexpressed in 50.8% and 27.1% of isolates studied, respectively. Overexpression of the MexEF-OprN and MexCD-OprJ systems was not observed. AmpC β-lactamase was overexpressed in 11.9% of P. aeruginosa isolates. In addition, decreased oprD expression was also observed in 69.5% of the whole collection, and in 87.1% of the imipenem non-susceptible P. aeruginosa clinical isolates. The MBL-encoding genes blaSPM-1 and blaIMP-1 were detected in 23.7% and 1.7% P. aeruginosa isolates, respectively. The blaGES-1 was detected in 5.1% of the isolates, while blaGES-5 and blaCTX-M-2 were observed in 1.7% of the isolates evaluated. In the present study, we have observed that efflux systems represent an adjuvant mechanism for antimicrobial resistance.ConclusionsEfflux systems in association of distinct mechanisms such as the porin down-regulation, AmpC overproduction and secondary β-lactamases play also an important role in the multi-drug resistance phenotype among P. aeruginosa clinical isolates.
Highlights
Multi-drug efflux pumps have been increasingly recognized as a major component of resistance in P. aeruginosa
Bacterial efflux systems capable of ejecting antimicrobials are mostly encoded by chromosomal genes and generally fall into five classes, the major facilitator superfamily (MFS), the ATP-binding cassette (ABC)
The efflux systems MexCD-OprJ and MexEF-OprN are quiescent in wild type P. aeruginosa, their overexpression may contribute to the acquired multi-drug resistance phenotype in mutant isolates [5]
Summary
Multi-drug efflux pumps have been increasingly recognized as a major component of resistance in P. aeruginosa. Pseudomonas aeruginosa is an aerobic gram-negative pathogen and a common etiologic agent of nosocomial infections, especially pneumonia, in seriously ill patients [1,2]. MexAB-OprM and MexXY-OprM are constitutively expressed and contribute to the intrinsic resistance phenotype of P. aeruginosa. When overexpressed, these efflux systems confer reduced susceptibility to different classes of antimicrobial agents [7,8]. The efflux systems MexCD-OprJ and MexEF-OprN are quiescent in wild type P. aeruginosa, their overexpression may contribute to the acquired multi-drug resistance phenotype in mutant isolates [5]
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