Nano‐Encapsulated <i>Cinnamomum cassia</i> Essential Oil in Combination With Fluconazole Exhibits Synergistic Activity Against Fluconazole‐Resistant <i>Nakaseomyces glabratus</i> and <i>Pichia kudriavzevii</i>

BACKGROUND: Nakaseomyces species, particularly Nakaseomyces glabratus and Pichia kudriavzevii, pose remarkable treatment challenges due to their resistance to common antifungal agents like fluconazole (FCZ). Essential oils, such as Cinnamomum cassia essential oil (CC-EO), offer a promising alternative, especially when enhanced with nanotechnology to improve stability and bioavailability. AIM: This study aims to evaluate the antifungal efficacy of CC-EO and its nano-encapsulated form (nano-CC-EO) against Nakaseomyces spp. to explore their potential as alternative treatments for resistant candidiasis. METHODS: Ten clinical isolates of N. glabratus and P. kudriavzevii were tested using CC-EO and nano-CC-EO, which were prepared via nanoprecipitation. Antifungal efficacy was evaluated through disk diffusion, microdilution and checkerboard assays, whereas nano-CC-EO's physicochemical properties were characterized using dynamic light scattering, scanning electron microscopy and zeta potential analysis. RESULTS: Characterization of nano-CC-EO showed an average particle size of 174.8 nm and a stable zeta potential of -18.6 mV, confirming uniformity and stability. In disk diffusion screening, nano-CC-EO produced larger inhibition zones than CC-EO at 2000 ppm, providing a qualitative indication of stronger growth inhibition. Microdilution tests revealed minimum inhibitory concentration (MIC) values of 250-500 ppm for nano-CC-EO and 125-500 ppm for CC-EO, highlighting strong inhibitory effects against Nakaseomyces isolates. Checkerboard assays demonstrated synergistic and additive interactions between nano-CC-EO and FCZ, with several isolates showing fractional inhibitory concentration index (FICI) values below 0.5. CONCLUSION: This study highlights the enhanced antifungal potential of nano-CC-EO, offering a promising alternative for treating resistant Nakaseomyces infections. Nano-CC-EO formulations demonstrated superior efficacy and targeted delivery, suggesting their potential as effective natural antifungal agents.