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Background and purpose: The increasing emergence of multidrug resistance among Klebsiella pneumoniae nosocomial isolates has limited the therapeutic options in treatment of infections caused by these bacteria. The beta-lactamases, efflux pumps and porins constitute the major defense mechanisms of antibiotic resistance of these bacteria. The aims of the present study were detection of OqxA and OqxB genes, evaluation of expression level of OqxA efflux pump and also determining the genetic basis of resistant K. pneumoniae strains isolated from hospitalized patients in Mofid and Taleghani hospitals during 2011-2012. Materials and methods: This study was conducted in 100 K. pneumoniae isolates from Taleghani and Mofid hospitals in Tehran, Iran. Antibiotic susceptibility tests were performed by Kirby- Bauer disc diffusion and Broth Microdilution methods according to CLSI guidelines. Detection of extended spectrum beta-lactamases was done by a kit developed by MAST group. The Modified Hodge Test (MHT) was used to identify carbapenemase production among the isolates. The OqxA and OqxB genes were detected by PCR and sequencing methods and oqxA gene expression was analyzed using realtime RT–PCR. PFGE typing was then performed for further analysis of the resistant isolates. Results: Among 100 K. pneumoniae isolates, 5(5%) were KPC positive and 48(48%) were ESBL positive. In this study, fosfomycin, colistin and tigecycline were found more effective than other antibiotics. The prevalence of both oqxA and oqxB genes detected among the K. pneumoniae isolates was 50 (50%). RT– PCR revealed higher expression (2.3-fold) in isolates with reduced susceptibility to Ciprofloxacin. Isolates belonged to three clusters and some of them belong to a particular clone. Conclusion: The prevalence of antibiotic resistance genes identified in this study highlights the need for more infection control measures including antibacterial management and identification of resistant isolates.

Keywords: Klebsiella pneumoniae, β-Lactamases, efflux pumps, antibiotic resistance

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