Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 10 3-4 2021 10 23 1 10 Ali Shivaee Department of Microbiology, faculty of Medicine, Iran University of Medical Sciences,Tehran, Iran Soheila Kashani Department of Science, Faculty of Sciences, Tehran Central Branch, Islamic Azad University, Tehran, Iran Rokhsareh Mohammadzadeh Department of Microbiology, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran Maryam Ebrahimi Department of Science, Faculty of Sciences, Tehran Central Branch, Islamic Azad University, Tehran, Iran 2019 03 17 Background:     Nanoparticles are a new generation of antimicrobials. Zinc oxide nanoparticles have attracted a great deal of interest in their medical applications. The aim of the present study was to investigate the effect of zinc nanoparticles on the expression of mrkA and fimA genes in drug-resistant K. pneumoniae. Methods:     A total of 30 clinical isolates of K. pneumoniae were collected from Sina hospital and all the isolates were identified by biochemical tests. Antimicrobial resistance pattern was determined by disk diffusion method. PCR method was used to investigate the presence of mrkA and fimA genes. Biofilm phenotypic test was performed and after conducting MIC test by micro dilution method, real-time PCR was used to study the effect of zinc oxide nanoparticle on the expression of fimA and mrkA genes. Results:     The highest resistance rate was against cefotaxime and ceftazidime antibiotics (67%). Twenty seven isolates harbored fimA gene while 24 isolates harbored mrkA gene. Five isolates were identified as strong biofilm producers. MIC values for zinc oxide was 2500 µg/ml in all five isolates. Results of real-time PCR showed that the expression levels of mrkA and fimA genes in isolates treated with zinc oxide decreased 8.5 and 9 fold, respectively, compared with the control. Conclusion:     This study suggests that zinc oxide can be a suitable candidate for the inhibition of the two studied virulence genes in K. pneumoniae. https://jmb.tums.ac.ir/index.php/jmb/article/view/415 https://jmb.tums.ac.ir/index.php/jmb/article/download/415/342