Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 50 11 2021 10 16 2292 2301 Maryam Mehdizadeh Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Mojgan Sheikhpour Department of Mycobacteriology and Pulmonary Research, Pasteur Institute of Iran, Tehran, Iran AND Microbiology Research Center, Pasteur Institute of Iran, Tehran, Iran Iman Salahshourifar Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Seyed Siadat Department of Mycobacteriology and Pulmonary Research, Pasteur Institute of Iran, Tehran, Iran AND Microbiology Research Center, Pasteur Institute of Iran, Tehran, Iran Parvaneh Saffarian Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran 2021 08 08 2021 10 06 Background: We aimed to prepare a nanofluid, containing f-MWCNTs, and investigate the antibacterial efficacy of f-MWCNTs+ ciprofloxacin (cip) on Klebsiella pneumoniae by evaluating the virulence gene expression. Methods: This study was carried out from 2019 to 2020, in the Department of Mycobacteriology and Pulmonary Research, Pasteur Institute of Iran. The nanofluid containing antibiotic and f-MWCNTs were prepared by the ultrasonic method. The minimum inhibitory concentrations (MICs) of ciprofloxacin and f-MWCNTs were determined using the broth micro dilution MIC tests. For examining the antibacterial effects, the expression level of virulence genes, under the influence of f-MWCNTs, was evaluated by a real-time PCR. Results: The effect of 8 µg/ml ciprofloxacin + 400 µg/ml f-MWCNTs, completely inhibited the growth of the resistant isolate of K. pneumoniae, while, in the ATCC 700,603 isolate, 2 µg/ml ciprofloxacin with 100 µg/ml f-MWCNT could inhibit a bacterial growth. In the resistant K. pneumoniae clinical isolate, after f-MWCNT+cip treatment, the expression of fimA, fimD, wza, and wzi genes was significantly downregulated, compared to the ciprofloxacin treatment, and upregulated, compared to the negative control. For the ATCC 700,603 isolate treated with f-MWCNT+cip, the expression of fimA, fimD and wza virulence genes showed upregulation, compared to the negative control and downregulated in comparison with the ciprofloxacin treatment. Conclusion: Simultaneous treatment of resistant isolate of K. pneumoniae with f-MWCNTs +antibiotic could improve the effectiveness of antibiotic at lower doses, due to the reduced expression of virulence genes in comparison with antibiotic treatment, besides the increased cell wall permeability to antibiotics. https://ijph.tums.ac.ir/index.php/ijph/article/view/25850 https://ijph.tums.ac.ir/index.php/ijph/article/download/25850/7414