Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 8 1 2016 03 01 55 61 EN Davood Mansury Department of Bacteriology and Virology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran AND Antimicrobial Resistance Research Center, Avicenna Research Institute, Mashhad University of MedicalSciences, Mashhad, Iran. Mohammad Motamedifar Department of Bacteriology and Virology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran AND Shiraz HIV/AIDS Research Center, Shiraz University of Medical Sciences, Shiraz, Iran. Jamal Sarvari Department of Bacteriology and Virology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. Babak Shirazi Department of Pathology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. Azad Khaledi Antimicrobial Resistance Research Center, Avicenna Research Institute, Mashhad University of MedicalSciences, Mashhad, Iran. 2015 10 31 2015 12 03 Background and Objectives: Klebsiella pneumoniae, one of the important causes of nosocomial infections, is the most common extended spectrum β-lactamases (ESBLs) producing organism. ESBLs are defined as the enzymes capable of hydrolyzing oxyimino-cephalosporins, monobactams and carbapenems. The aims of this study were to identify ESBL-producing K. pneumoniae isolates and detect their antibiotic susceptibility pattern. Materials and Methods: This cross-sectional study was conducted from December 2012 to May 2013 in teaching hospitals in Shiraz. Clinical specimens from the urine, sputum, wound, blood, throat, and body fluids were isolated and identified as K. pneumoniae. Antibacterial susceptibility testing was performed for 14 antibiotics using disk diffusion method according to CLSI guidelines. Isolates showing resistant to at least one of the β-lactam antibiotics were then evaluated for production of β-lactamase enzymes using E-test ESBL and combined disk Method. Also, MICs for ceftazidime and imipenem were determined using E-test. The presence of the blaSHV, blaTEM٫ blaPER and blaCTX-M genes was assessed by PCR. Results: Of 144 K. pneumoniae isolates from different specimens, 38 (26.3 %) was identified as ESBL producer by phenotypic confirmatory test. All ESBL producing isolates were susceptible to imipenem and meropenem and resistant to aztreonam. The highest rate of resistance belonged to amoxicillin (100%), cefotaxime (50%) and gentamicin (42.3%) and the lowest rates were seen for meropenem (11.8%), imipenem and amikacin (both 15.9%). Sixty-two isolates had MICs≥ 4 μg/ mL for ceftazidime, of which 38 were positive for ESBLs in phenotypic confirmatory tests (PCT). The prevalence of blaSHV, blaCTX-M, and blaTEM genes among these isolates were 22.2%, 19% and 16%. blaPER was not detected in the studied isolates. Conclusions: Due to the relatively high prevalence of ESBLs-producing K. pneumoniae isolates in the studied population, it seems that screening of infections caused by ESBL producers can lead to the most effective antibiotics therapies. https://ijm.tums.ac.ir/index.php/ijm/article/view/767 https://ijm.tums.ac.ir/index.php/ijm/article/download/767/561