Fungicidal activity of grapefruit seed extract against the pathogenic Candida species causing oral candidiasis

This study aimed to evaluate the antifungal activity of grapefruit seed extract (GSE) against Candida species and to confirm the biological safety. Two-fold serial dilutions of GSE or miconazole were prepared. Cell suspensions of Candida albicans, Candida glabrata, Candida tropicalis, or Candida parapsilosis were added to each diluted solution, and the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) were determined. The MFC/MIC ratio was calculated to determine whether the substance had a fungistatic or fungicidal activity. Each Candida species treated with GSE were examined using a scanning electron microscope (SEM) and fluorescence microscopy. The effect of GSE on EpiOral™, a three-dimensional tissue model, was assessed by tissue viability assay and histological analysis. GSE was applied to the mandibular gingiva of Japanese white rabbits, and the gingival tissues were histopathologically assessed. GSE demonstrated a fungicidal effect against all tested Candida species, whereas miconazole demonstrated a fungicidal effect against only C. albicans. SEM images showed various cell damage patterns in GSE-treated Candida cells. Fluorescence microscopy revealed that almost all Candida cells were killed by GSE-treated. EpiOral™ treated with GSE showed no effect on the tissue viability and there was no remarkable difference between GSE and control groups in the histological analysis. The histopathological observation in the oral mucosa treated with GSE showed no significant histopathological changes. Taken together, GSE has a fungicidal activity against C. albicans, C. glabrata, C. tropicalis, and C. parapsilosis, and no adverse effects were observed in vitro and in vivo.