Evaluation of chromosomally and acquired mechanisms of resistance to carbapenem antibiotics among clinical isolates of Pseudomonas aeruginosa in Kerman, Iran

Introduction: Multidrug-resistant (MDR) of Pseudomonas aeruginosa isolates are increasing around the world which can cause serious problems for antimicrobial therapy in hospital settings. Our aim in present study was to evaluation of intrinsic and acquired mechanisms of resistance to carbapenem antibiotics among 170 clinical isolates of P. aeruginosa in Kerman, Iran. Material and methods: CLSI recommendations were used for determination of antimicrobial susceptibility testing of isolates. Metallo-beta-lactamase (MBL) producing isolates were detected by the double-disc synergy test (DDST) using the 2-mercaptopropionic acid and efflux pump over-activity were determined by the microdilution method using PabN. PCR-sequencing technique was used for to detection and sequencing of carbapenemase, bla(CTX-M) and oprD genes. Transcriptional levels of the mexA gene in carbapenem-resistant isolates was evaluated by qRealtime PCR (qPCR) and ERIC-PCR technique was used for molecular typing of carbapenem-resistant isolates. Results: According to our findings, colistin was the most active agent against P. aeruginosa isolates. All carbapenem-resistant P. aeruginosa were efflux pumps overproducers and 4.92% isolates were MBL producing. The MBL genes including: bla(NDM), bla(VIM), bla(IMP) and bla(SIM) were detected in (2, 3.3%), (1, 1.6%), (1, 1.6%), (1, 1.6%), of the isolates, respectively. The oprD gene was disrupted in 9 isolates by insertion sequences (ISs). The qPCR experiment showed that transcriptional levels of mexA gene in 26 (42.6%) carbapenem-resistant P. aeruginosa have more than 2-7-fold change with comparison to P. aeruginosa PAO1 strain. ERIC-PCR results was showed 10 clusters and 6 singletons in carbapenem-resistant isolates. Conclusions: In this study, we reported bla(NDM-1) and bla(SIM) positive P. aeruginosa isolates for the first time in Kerman, Iran. Furthermore, our results were showed that intrinsic resistance mechanisms including over expression of efflux pump and inactivation of oprD have an important role in resistance to carbapenem antibiotics in clinical isolates of P. aeruginosa in Kerman, Iran.