Synergistic Antifungal Effects of Honokiol and Fluconazole Against Oral Candida : Implications for Managing Drug‐Resistant Infections

OBJECTIVES: Antifungal drug resistance poses a major challenge in treating oral Candida infections. This study aimed to evaluate the antifungal activity of Honokiol, alone and combined with Fluconazole, against oral Candida isolates, and to investigate its mechanism of action via ergosterol biosynthesis inhibition and cell wall disruption. MATERIAL AND METHODS: Susceptibility testing was performed using CLSI (M27-A3) methodology on 16 oral Candida isolates, 8 endodontic isolates, and the reference strain ATCC 24433. Minimum inhibitory concentrations (MICs) of Honokiol and Fluconazole were determined alone and in combination. Ergosterol inhibitory assays and scanning electron microscopy (SEM) were used to assess cell wall integrity and morphological changes. RESULTS: Honokiol exhibited MICs of 16-64 µg/mL (oral isolates), 16 µg/mL (endodontic isolates), and 32 µg/mL (ATCC 24433). In combination with Fluconazole, Honokiol's MICs decreased 4-fold (4-16 µg/mL), while Fluconazole's MICs dropped 2- to 4-fold (1-32 µg/mL). Synergy was confirmed by a 95.61% reduction in fungal growth (OD600) compared to controls. SEM revealed severe cell wall distortion, rupture, and cytoplasmic leakage. Honokiol significantly inhibited ergosterol biosynthesis, disrupting cellular integrity. CONCLUSION: Honokiol demonstrates potent antifungal activity against oral Candida isolates by targeting ergosterol biosynthesis and compromising cell wall integrity. Its synergistic enhancement of Fluconazole's effect suggests clinical potential as an adjunct therapy, potentially reducing resistance and lowering required drug doses in oral and endodontic candidiasis.