Growth inhibition and ultrastructural alterations induced by Δ²⁴⁽²⁵⁾-sterol methyltransferase inhibitors in <it>Candida </it>spp. isolates, including non-<it>albicans </it>organisms

• Main Authors: Nakamura Celso, Urbina Julio A, de Souza Wanderley, Vila Taíssa, Ribeiro Marcos, Rodrigues Juliany, Ishida Kelly, Rozental Sonia
• Format: Article
• Language: English
• Published: BMC 2009-04-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/9/74

<p>Abstract</p> <p>Background</p> <p>Although <it>Candida </it>species are commensal microorganisms, they can cause many invasive fungal infections. In addition, antifungal resistance can contribute to failure of treatment.</p> <p>The purpose of this study was to evaluate the antifungal activity of inhibitors of Δ²⁴⁽²⁵⁾-sterol methyltransferase (24-SMTI), 20-piperidin-2-yl-5α-pregnan-3β-20(R)-diol (AZA), and 24(R,S),25-epiminolanosterol (EIL), against clinical isolates of <it>Candida </it>spp., analysing the ultrastructural changes.</p> <p>Results</p> <p>AZA and EIL were found to be potent growth inhibitors of <it>Candida </it>spp. isolates. The median MIC₅₀was 0.5 μg.ml^-1for AZA and 2 μg.ml^-1for EIL, and the MIC₉₀was 2 μg.ml^-1for both compounds. All strains used in this study were susceptible to amphotericin B; however, some isolates were fluconazole- and itraconazole-resistant. Most of the azole-resistant isolates were <it>Candida </it>non-<it>albicans </it>(CNA) species, but several of them, such as <it>C. guilliermondii, C. zeylanoides</it>, and <it>C. lipolytica</it>, were susceptible to 24-SMTI, indicating a lack of cross-resistance. Reference strain <it>C. krusei </it>(ATCC 6258, FLC-resistant) was consistently susceptible to AZA, although not to EIL. The fungicidal activity of 24-SMTI was particularly high against CNA isolates. Treatment with sub-inhibitory concentrations of AZA and EIL induced several ultrastructural alterations, including changes in the cell-wall shape and thickness, a pronounced disconnection between the cell wall and cytoplasm with an electron-lucent zone between them, mitochondrial swelling, and the presence of electron-dense vacuoles. Fluorescence microscopy analyses indicated an accumulation of lipid bodies and alterations in the cell cycle of the yeasts. The selectivity of 24-SMTI for fungal cells versus mammalian cells was assessed by the sulforhodamine B viability assay.</p> <p>Conclusion</p> <p>Taken together, these results suggest that inhibition of 24-SMT may be a novel approach to control <it>Candida </it>spp. infections, including those caused by azole-resistant strains.</p>