Expression of MexAB-OprM efflux pump system and meropenem resistance in Pseudomonas aeruginosa isolated from surgical intensive care unit

Abstract

Background: Meropenem resistance of Pseudomonas aeruginosa (P. aeruginosa) is considered an increasing problem. Efflux pump is one of multiple mechanisms that are responsible for this resistance. This study aimed to phenotypically and genotypically detect prevalence of efflux pump mediated meropenem resistance among P. aeruginosa isolates.

Methods: Pseudomonas aeruginosa was isolated from different clinical specimens and identified by conventional methods and confirmed by Viètek MS Malditof Mass Spectroscopy. Antibiotic susceptibility test was done by disc diffusion method then minimum inhibitory concentrations (MIC) for meropenem was detected twice by agar dilution method without and after addition of carbonyl cyanide m-chlorophenylhydrazone (CCCP). Efflux pump genes were detected by polymerase chain reaction (PCR).

Results: Out of 265 specimens, 78 P. aeruginosa were isolated with an isolation rate (29.4%). By disc diffusion method and MIC by agar dilution methods, 35 (44.8%) isolates were meropenem resistant. There was a significant difference regarding distribution of efflux pump genes in meropenem resistant isolates as 23 isolates (65.7%) were positive for efflux pump genes and 12 (34.3%) were negative (p value= 0.13). The MICs of meropenem for P. aeruginosa isolates were significantly decreased after addition of CCCP where MIC of 21 (60%) meropenem resistant isolates had an efflux pump-overexpressing phenotype (p value =0.001).

Conclusion: High prevalence of meropenem resistance in P. aeruginosa is mediated by efflux pump genes including, mex A, mex B and opr M.