Ethanolic extract of Polish Propolis exhibits synergy with selected antifungal agents against yeast pathogens causing candidiasis

Candidiasis pose a serious health threat, stimulating efforts to develop new antifungal agents and alternative therapies. Given the high mortality of fungal infections and the historical use of natural remedies, there is a growing interest in integrating natural substances into modern treatments. It is particularly important to explore interactions between home remedies and clinically approved antifungals to avoid harmful combinations or enhance beneficial effects. In this study, the chemical composition of the ethanolic extract of propolis (EEP) using UHPLC-DAD-QqTOF-MS was analyzed. The interactions of this extract with several antifungal agents against four yeast pathogens causing candidiasis: Candida albicans, Nakaseomyces glabratus, Pichia kudriavzevii, and Candida auris were investigated using Checkerboard Titration Assay, Growth Kinetics, and Disc-diffusion assay. Also, a novel simulated infection model was proposed. The results showed synergistic interactions between EEP and amphotericin B, and additive effects with nystatin. Synergy and additivity with fluconazole and voriconazole were observed, but limited to C. albicans and N. glabratus. In contrast, antagonistic interactions were noted with caspofungin, clotrimazole, and ketoconazole, which may have clinical relevance. Additionally, positive interactions with 2-phenoxyethanol and silver nanoparticles (AgNPs) suggest potential practical applications. Propolis's synergistic properties could expand antifungal strategies and support the development of multi-target, resistance-preventing therapies.