Molecular Epidemiology and Mechanisms of High-Level Resistance to Meropenem and Imipenem in Pseudomonas aeruginosa

Purpose: Pseudomonas aeruginosa possesses a large number of resistance mechanisms to different antimicrobials with carbapenems being the most powerful in treating resistant P. aeruginosa. Hence, it is imperative to explore different mechanisms of carbapenemsresistance in P. aeruginosa to achieve successful treatment through the design of new drugs acting on this interaction to combat against antimicrobial resistance. Strains and Methods: A total of 634 P. aeruginosa clinical isolates were collected from various patient sources and their MIC levels were measured. Molecular evaluation of carbapenem resistance was assessed by investigating the presence of bla(IMP1), bla(IMP2), bla(VIM1), bla(VIM2), bla(NDM) and b/a NDm genes and the gene expression of the following multidrug efflux pump systems: MexAB-OprM, MexCD-OprJ, MexEF-OprN and MexXY-OprM and its correlation with MIC. Isolates were typed by Random Amplified Polymorphic DNA (RAPD)-typing. Results: Carbapenem resistance was detected in 32 (5%) isolates, which were all imipenem resistant (of which 29 were meropenem resistant). High-level resistance (>= 64mg/mL) to imipenem was found in 27 (84.3%) isolates, and to meropenem in 28 (96.5%) isolates. The carbapenemase bla(VIM-1) was found in 31 isolates, while bla(NDM) was detected in 4 isolates. None of the isolates possessed either bla(VIM-2), bla(IMP-1), bla(IMP-1) or bla(SPM). The majority of the isolates displayed over-expression of MexCD-OprJ (75%) followed by MexXY-OprM efflux pump (62%), while MexAB-OprM and MexEF-OprN efflux pumps were overexpressed in 21.8% and 18.7% of the isolates, respectively, with no down-regulation of oprD in any of the isolates. A strong correlation was found between CDJ efflux pump expression and meropenem, imipenem resistance (r=0.532, 0.654, p<0.001, <0.001) respectively. Four major clusters were detected by RAPD-typing: group 1(10 isolates), group 3 (9 isolates), group 2 (8 isolates) while the fourth group (4) included 4 isolates (12.5% polymorphism). Conclusion: High-level carbapenem resistance reported in this study was allied to multiple mechanisms including carbapenemase production and efflux-pump over-expression. Threatening cross-infection is possible inside the hospital and stringent infection control measures are crucial.