Role of efflux pump and OprD porin expression in carbapenem resistance of Pseudomonas aeruginosa clinical isolates

Introduction: In recent years, the prevalence of multidrug-resistant P. aeruginosa has remarkably increased. Thus, we wanted to investigate the carbapenem resistance mechanisms and clonal relationship among 80 carbapenem-resistant P. aeruginosa strains. Methodology: Carbapenemase production was detected using the Modified Hodge Test (MHT), EDTA combined disc method (ECD), and PCR. Expression levels of efflux and porin genes were mesured by real-time reverse transcription PCR. Clonal relationship of the isolates was investigated by pulsed-field gel electrophoresis (PFGE). Results: Carbapenemase production was detected in 7.5% of the isolates with MHT/ECD tests and in 11.3% of the isolates with PCR. Although the specificity of MHT/ECD was high, the sensitivitivity was low. oprD downregulation and mexB, mexY, and mexD overexpression were demonstrated in 55%, 16.3%, 2.5%, and 2.5% of the isolates, respectively. Multiple carbapenem resistance mechanisms were found in nearly a quarter of the isolates. PFGE typing of the 80 P. aeruginosa isolates yielded 61 different patterns. A total of 29 isolates (36.3%) were classified in 10 clusters, containing 2 to 7 strains. We could not find a strict relationship between PFGE profile and carbapenem resistance mechanisms. Conclusions: Although oprD downregulation and MexAB-OprM overexpression were the most common mechanisms, carbapenem resistance was associated with multiple mechanisms in the study. MHT/ECD tests should not be used alone for investigation of carbapenemase production in P. aeruginosa. Rapid tests with high sensitivity and specificity should be developed for the detection of carbapenemase production in P. aeruginosa.