Synergistic antifungal activity and mechanism of piroctone olamine and sorbitan caprylate against Malassezia restricta

AIMS: Malassezia restricta is a lipid-dependent opportunistic pathogen that is associated with various skin disorders including seborrheic dermatitis, dandruff, and tinea versicolor. This study aimed to investigate the antifungal activity and mechanism of piroctone olamine (OCT) and sorbitan caprylate (SC) in combination against M. restricta. METHODS AND RESULTS: The combination of 3.125 μg ml-1 OCT and 0.39 μg ml-1 SC effectively inhibited the growth of M. restricta. Microscopic observation of the fungal morphology, propidium iodide staining assay, and content leakage test indicate that the combinations OCT-SC complex 5 (OCT: SC = 4:1, OS-5) and OCT-SC complex 9 (OCT: SC = 8: 1, OS-9) effectively disrupt the cell membrane of M. restricta. Crystal violet staining experiments show that these combinations inhibit biofilm formation of M. restricta, which helps reduce its survival on the surface of mammalian skin. Reverse transcription quantitative PCR and HPLC assays reveal that after treatment with the combinations, genes involved in ergosterol synthesis and cell membrane formation in M. restricta are upregulated, whereas the fungal ergosterol content is markedly reduced, suggesting a compensatory transcriptional response to inhibited ergosterol synthesis. CONCLUSION: OCT-SC combinations exert strong antifungal activity against M. restricta by disrupting the cell membrane and inhibiting biofilm formation and reducing ergosterol content despite upregulation of related genes. The results highlight their potential as promising candidates for antifungal drug development. They may also serve as active ingredients in personal care products targeting skin diseases caused by M. restricta.