MOJDEH HAKEMI-VALA¹, HELIA OSTADASADI -MALAYERI², MEHRDAD GHOLAMI³, HOSSEIN GOUDARZI<sup>1

1</sup>Department of microbiology, medical school, Shahid Beheshti university of medical sciences Tehran-Iran, ²Department of Microiology, Faculty of Basic Sciences, Sanandaj branch, Islamic Azad University, Sanandaj-Iran , ³PhD candidate, Iran university of medical sciences Tehran-Iran

Background: Acinetobacter baumannii (A. baumannii) has emerged as a highly problematic hospital-associated pathogen and it can be an opportunistic pathogen in humans and affecting people with compromised immune systems[1]. This study aims to evaluate the role of efflux pump regulators and OXA-23 genes in imipenem resistance A. baumannii strains isolated from hospitalized patients.

Material/methods: This study was conducted on 60 A. baumannii isolates collected from patients admitted to the Shahid Motahari and Taleghani Hospitals in Tehran during 2013-14. Antibiotic susceptibility tests (AST) and minimal inhibitory concentration (MIC) was determined by broth micro dilution methods according to CLSI 2014 guidelines [2]. The frequency of efflux pump adeRS and OXA-23 genes were detected by PCR and further sequencing.

Results: The resistance of A. baumannii isolates to tested antibiotics was (100%) to cefotaxime, ceftazidime, ceftriaxone, ciprofloxacin, cefepime, piperacillin, meropenem, co-trimoxazole and piperacillin/tazobactam, (97 %) to imipenem, (94%) to gentamicin, (83%) to amikacin, (76%) to tetracycline, and (0.0%) to colistin. The MIC of 58 (96.6%) strains to imipenem was highly decreased in the presence of efflux pump inhibitor (PaβN), by 4 to 64 folds. The adeR and adeS genes were detected in 36 (60%) and 59 (98.3%), respectively and the frequency of OXA-23 gene was 57 (95%) of isolates.

Conclusions: Existence of adeRS and OXA-23 genes in more than 50% of A. baumannii isolates in this study shows the presumptive role of efflux pump in simultaneous of carbapenemase production. So, using new strategies are required in order to stop the vertical or horizontal exchanges mentioned genes from the resistant A. baumannii isolates to sensitive strains. Also doing antimicrobial susceptibility test before any prescription can decrease the emergence of resistant bacteria. However, all tested A. baumannii isolates in this study were susceptible to colistin, hopefully.

Key words: Acinetobacter baumannii, oxa23 beta-lactamase, drug resistance, efflux pumps