ABSTRACT
Background: Pseudomonas aeruginosa [P. aeruginosa] is a major cause of hospital-acquired infections, especially in intensive care units. These infections represent a very difficult therapeutic challenge and are associated with significant morbidity and mortality. This is due to the high level of natural and acquired resistance of this organism. The incidence of multidrug resistant [MDR] isolates of P. aeruginosa is currently increasing. Overexpression of multidrug efflux pumps [EPs] is one of the most important underlying mechanisms. These efflux pumps can extrude antibiotics from the cytoplasm or periplasmic space into the extracelluar milieu leading to suboptimal intracellular concentration and consequently loss of drug efficacy. Aim: The aim of this work was to assess the prevalence of efflux pump overexpression among clinical isolates of P. aeruginosa and its contribution in MDR phenotype. Also, to measure the impact of using an efflux pump inhibitor [EPI]; phenylalanine-arginine- beta -naphthylamide [PAbetaN] on the minimal inhibitory concentration [MIC] of ciprofloxacin [CIP]. The results obtained would help to develop a new therapeutic strategy that targets efflux pump and depends on the concomitant administration of an antibiotic with an efflux pump inhibitor in order to restore the antibiotic activity
Methods: Twenty eight P. aeruginosa isolates were collected from blood cultures, pulmonary samples, urine and infected pressure ulcers from patients in the intensive care unit and from nose, ear and middle meatus swabs from patients in ENT department. Multidrug efflux pumps overexpression by these isolates was detected using real time PCR for detection of four efflux pump genes; mexB, mexD, mexF and mexY. For evaluating the effect of EPI; PAbetaN on MIC of CIP, E test for CIP was done in the absence and in the presence of PAbetaN
Results: The results of the present study showed that 22 [78.6%] P. aeruginosa isolates overepressed at least one of the 4 measured efflux pump genes with mexB the most prevalent gene; 19 isolates [75%] followed by mexY; 3 isolates [10.7%], then mexF one isolate [3.5%]. One isolate showed simultaneous expression of mexB and mexY and one isolate expressed mexF together with both mexB and mexY. None of the isolates overexpressed mexD gene. Overexpression of EP was significantly higher in MDR isolates than non MDR isolates. Addition of the EPI, PAbetaN, resulted in significant reduction in the median of the MIC of CIP in 20 [71.4%] isolates
Conclusion: Efflux pump-mediated resistance was a significant mechanism contributing to multidrug resistance in clinical isolates of P. aeruginosa, however, other drug resistance mechanisms should be considered. Although the addition of EPI; PAbetaN resulted in lowering of the MIC of CIP in both CIP sensitive and CIP resistant strains, only few isolates reverted from CIP resistant into CIP sensitive ones. It is, therefore, important to continue the exploration of more effective EPIs and large-scale surveillance studies are recommended to detect the true prevalence of efflux pump overexpression as well as other possible mechanisms among P. aeruginosa isolates and their link with multidrug resistance