en باکتری شناسی Bactriology پژوهشي Research <strong>Background and Aims: </strong>Extended-spectrum &beta;-lactamase (ESBL) producing gram negative bacteria are resistant to penicillins, narrow and extended-spectrum cephalosporins, and aztreonam; also they are frequently resistant to trimethoprim-sulfamethoxazole, aminoglycosides, and quinolones. This study aimed to investigate the prevalence of plasmid-mediated quinolone resistance (PMQR) determinants <em>qnr</em>A, <em>qnr</em>B and <em>qnr</em>S in ESBL producing<em> Klebsiella pneumoniae </em>isolates.<br> <strong>Materials and Methods:</strong> In this descriptive-sectional study, 130 <em>Klebsiella pneumoniae</em> isolates were collected from urine specimens and identified by convectional biochemical tests from December 2013 to August 2014,. Antimicrobial susceptibility testing was performed by disk diffusion method (Kirby-Bauer). The presence of ESBLs was confirmed by combination disk tests. E.test method was used for determination of ceftazidime and ciprofloxacin minimum inhibitory concentration (MIC). <em>qnr</em> genes were investigated by multiplex polymerase chain reaction and after sequencing, indexed in Genbank database.<br> <strong>Results: </strong>Out of 130 isolates, 46 (35.4%) isolates were identified as ESBL producers, considering all, the highest rate of resistance belonged to amoxicillin, cefotaxime and ceftriaxone (each one 100%) and the lowest rate of resistance was for meropenem and ertapenem (each one 4.3%). 45 (97.8%) isolates were resistant to ceftazidime (MIC <span dir="RTL">&le;</span> 16) and 24 (52.2%) isolates were resistant to ciprofloxacin (MIC<span dir="RTL">&le;</span>4).<em> qnr</em>B and <em>qnr</em>S genes were detected in 21 (45.7%) and 7 (15.2%) isolates, respectively. 7 (15.2%) isolates were positive for both <em>qnr</em>B and <em>qnr</em>S genes. <em>qnr</em>A was not detected.<br> <strong>Conclusions:</strong> With respect to the high prevalence of <em>qnr</em> genes in ESBL producing<em> Klebsiella pneumoniae </em>isolates, quinolones and beta-lactam agents should be used with caution. ESBL, Klebsiella pneumoniae, PCR, qnr genes, Quinolone 25 33 http://ijml.ssu.ac.ir/browse.php?a_code=A-10-147-1&slc_lang=en&sid=1 Amin Dehghan Banadkouki amin_dehghan25@yahoo.com No Department of Medical Microbiology, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Gilda Eslami eslami_g2000@yahoo.com No Research Center for Food Hygiene and Safety, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Hengameh Zandi hengameh_zandi@yahoo.com Yes Research Center for Food Hygiene and Safety, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Ali Dehghan Banadkouki amin_dehghan25@yahoo.com No Laboratory of Imam Khomeini Hospital, Karaj, Iran.