Geraniol inhibits both planktonic cells and biofilms of the Candida parapsilosis species complex: Highlight for the improved efficacy of amphotericin B, caspofungin and fluconazole plus Geraniol

The Candida parapsilosis species complex poses a recognized threat to the nosocomial environment. In the scenario of the global rise of resistant strains to antifungals, geraniol, a terpene isolated from different essential oils, has shown promising antimicrobial activity. We evaluated: (1) the effects of geraniol against the C. parapsilosis species complex, in planktonic and biofilm forms; (2) the strains' susceptibility to clinical antifungals and (3) the geraniol interaction with antifungals. Eighteen isolates were subjected to in vitro susceptibility testing by the broth microdilution protocol, using geraniol, amphotericin B, caspofungin, itraconazole and fluconazole to determine the minimum inhibitory concentration (MIC) and subsequently, we measured the fungicidal activity. Geraniol was tested against biofilms by the measurement of the metabolic activity and biomass. Pharmacological interactions were performed by the checkerboard method. Geraniol's MIC range was between 256 and 512 µg/ml. MIC range for clinical antifungals was ≤ 0.031-4 µg/ml. Geraniol also showed antibiofilm activity with average reductions of metabolic activity (38.33%) and biomass (30.69%), at MIC concentration. Furthermore, geraniol showed synergistic/additive effects with antifungals. Briefly, geraniol inhibits both planktonic cells and biofilms of the C. parapsilosis species complex and besides it improves the efficacy of amphotericin B, caspofungin and fluconazole.