en Microbial pathogenesis Microbial pathogenesis Original article Original article <div style="text-align: justify;"><b><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">Introduction:</span></span></span></b><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times=""> Emerging drug-resistant fungal pathogens and the limitations of current antifungal therapies necessitate the development of alternative therapeutic strategies. This study aimed to investigate the effects of capsaicin on the growth and virulence factors of <i>Aspergillus fumigatus</i> AF293. <b>Methods:</b></span></span></span> <span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">The impact of capsaicin on fungal growth, ergosterol content, and gene expression was evaluated at concentrations up to 25 &mu;g/mL, and on biofilm formation at concentrations up to 100 &mu;g/mL. Expression levels of the <i>PLB1</i>, <i>PLB2</i>, <i>PLD1</i>, and <i>PLD2</i> genes were quantified using quantitative real-time PCR (qRT-PCR). <b>Results:</b> Capsaicin exhibited dose-dependent antifungal activity, inhibiting fungal growth (15.33&ndash;89.78%) and reducing ergosterol content (42.35&ndash;82.59%) at concentrations of 3.125&ndash;25 &mu;g/mL. The half-maximal inhibitory concentration (IC₅₀) for fungal growth was estimated to be between 6.25 and 12.5 &mu;g/mL. At the highest concentration tested (100 &mu;g/mL), biofilm formation was significantly suppressed by 88.34%. <i>PLB1</i> and <i>PLB2</i> gene expression was downregulated in a dose-dependent manner, with maximal reductions of 56% and 63%, respectively, at 25 &mu;g/mL.</span></span></span><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times=""> In addition, the expression of <i>PLD1</i> and <i>PLD2</i> genes decreased by 31.4% and 48.13%, respectively, at the highest tested concentration. <b>Conclusion: </b>Capsaicin demonstrates potent antifungal activity against <i>A. fumigatus</i> AF293 by inhibiting fungal<b> </b>growth, disrupting ergosterol biosynthesis, and reducing key virulence factors, including biofilm formation as well as <i>PLB</i> and <i>PLD</i> genes expression. These findings suggest that capsaicin is a promising lead compound for antifungal drug development.</span></span></span></div> Antifungal resistance, Aspergillus fumigatus AF293, Biofilm, Capsaicin, Ergosterol, Phospholipase B, Virulence factors 303 309 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-441-13&slc_lang=en&sid=1 Haniye Torkashvand zjahanshiri@yahoo.com 0009-0004-7179-3201 No Department of Mycology, Pasteur Institute of Iran, Tehran, Iran Zahra Jahanshiri z_jahanshiri@pasteur.ac.ir 0000-0001-9431-9335 Yes Department of Mycology, Pasteur Institute of Iran, Tehran, Iran