In vitro and in vivo analysis of monotherapy and dual therapy with ethyl caffeate and fluconazole on virulence factors of Candida albicans and systemic candidiasis

Objectives: Candida albicans is the most clinically prevalent cause of systemic fungal infections in the immunocompromised population. The biofilm-forming ability of C. albicans confers resistance to conven-tional antifungal agents. The main aim of this study was to investigate the antifungal effects of ethyl caffeate (EC) alone and in combination with fluconazole (FLU) against C. albicans isolates. Methods: The single and combined antifungal activities of EC and FLU were evaluated against planktonic and biofilm cells of C. albicans by the checkerboard assay, time-kill test, crystal violet assay, live/dead staining, rhodamine 6G (R6G) efflux analysis and hydrolase activity. Monotherapy and dual therapy of EC and FLU against systemic candidiasis in a mouse model was also evaluated. Results: The results showed that EC+ FLU displayed synergism in 14/26 planktonic C. albicans isolates and 11/26 C. albicans biofilms with fractional inhibitory concentration index (FICI) values ranging be-tween 0.06-0.49 and 0.02-0.38, respectively. Compared with monotherapy, the combination of EC+ FLU can markedly inhibit adhesion, yeast-to-hyphae transition, premature and mature biofilm metabolism, hydrolase secretion and drug efflux function of C. albicans Z1407 and Z4935. Moreover, EC can potentiate the antifungal activity of FLU to improve mouse survival, reduce fungal burden and alleviate pathological damage in both C. albicans isolates compared with EC or FLU used alone. Conclusion: EC exhibits a moderate antifungal potential but can be a strong synergist with FLU against C. albicans, highlighting the potential of EC in clinical antifungal therapy as a sensitiser. (C) 2021 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.