Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 14 1 2022 02 19 31 37 EN Mojtaba Niazadeh Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran Farhad Nikkhahi Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran Saeedeh Robatjazi Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran Amir Javadi Department of Biostatics, Qazvin University of Medical Sciences, Qazvin, Iran Seyed Amir Farzam Department of Pathology, Qazvin University of Medical Sciences, Qazvin, Iran Samaneh Babaei Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran Parisa Zeynali Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran 2020 08 24 2022 02 12 Background and Objectives: One of the major causes of urinary tract infections is Klebsiella pneumoniae. Currently, few studies investigated the mechanisms of resistance to colistin in Iran. The current study aimed to determine the prevalence of plasmid and chromosome-mediated resistance to colistin in K. pneumoniae isolates. Materials and Methods: 177 urine samples were collected from patients with urinary tract infections hospitalized in the intensive care unit (ICU) of hospitals in the city of Qazvin. K. pneumoniae isolates were identified by standard biochemical methods, resistance to colistin among K. pneumoniae isolates were tested by disk diffusion and microbroth dilution methods. The chromosomal mutation and presence of the mcr genes in colistin-resistant K. pneumoniae were evaluated by PCR. Results: Out of 177 samples, 65 K. pneumoniae were obtained from patients in the ICU. Six colistin-resistant isolates were isolated with MIC values ≥4 μg/mL, none of them was positive for mcr1-5. In 4 isolates, missense mutation in mgrB gene resulted in amino acid substitutions and in one isolate of mgrB gene was found intact mgrB gene. Conclusion: The results suggest that mgrB mutation was the main mutation among colistin-resistant isolates and plasmid-borne colistin resistance was not expanded among strains. https://ijm.tums.ac.ir/index.php/ijm/article/view/2758 https://ijm.tums.ac.ir/index.php/ijm/article/download/2758/1422