Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 15 1 2023 02 15 163 173 Zahra Jahanshiri Department of Mycology, Pasteur Institute of Iran, Tehran, Iran Soheila Manifar Department of Oral Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran Farahnaz Hatami Department of Cellular and Molecular Biology, Faculty of Advanced Science and Technology, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran 2022 09 08 2022 12 23 Background and Objectives: Candida tropicalis is one of the major non-albicans species causing nosocomial infection. There is limited data about mechanisms of azole-resistance and virulence factors of Candida tropicalis. This study was designed to investigate molecular mechanism of azole -resistance and major virulence factors of C. tropicalis isolated from oropharyngeal candidiasis in head and neck cancer patients. Materials and Methods: After collecting 38 C. tropicalis clinical isolates, antifungal susceptibility pattern and the expression levels of ERG11, CDR1, CDR2 and MDR1 were evaluated. Moreover, proteinase and phospholipase activity and biofilm formation of the isolates were investigated as virulence factors. Results: We detected fluconazole resistance in 7 C. tropicalis isolates. The expression levels of CDR1, ERG11 and MDR1 were increased respectively. Protease activity and biofilm formation were seen in all isolates. Five isolates did not exhibit phospholipase activity. Conclusion: Taken together, the overexpressions of ERG11, CDR1 and MDR1 genes were found in fluconazole resistant C. tropicalis, isolated from oropharyngeal candidiasis patients. Also, voriconazole was an effective antifungal against C. tropicalis isolates. The observed high protease enzyme activity and biofilm formation suggested strong pathogenicity of these isolates. https://ijm.tums.ac.ir/index.php/ijm/article/view/3895 https://ijm.tums.ac.ir/index.php/ijm/article/download/3895/1554