Optimum Inhibition of Amphotericin-B-Resistant Candida albicans Strain in Single- and Mixed-Species Biofilms by Candida and Non-Candida Terpenoids

Candida albicans is one of the most common human fungal pathogens and represents the most important cause of opportunistic mycoses worldwide. Surgical devices including catheters are easily contaminated with C. albicans via its formation of drug-resistant biofilms. In this study, amphotericin-B-resistant C. albicans strains were isolated from surgical devices at an intensive care center. The objective of this study was to develop optimized effective inhibitory treatment of resistant C. albicans by terpenoids, known to be produced naturally as protective signals. Endogenously produced farnesol by C. albicans yeast and plant terpenoids, carvacrol, and cuminaldehyde were tested separately or in combination on amphotericin-B-resistant C. albicans in either single- or mixed-infections. The results showed that farnesol did not inhibit hyphae formation when associated with bacteria. Carvacrol and cuminaldehyde showed variable inhibitory effects on C. albicans yeast compared to hyphae formation. A combination of farnesol with carvacrol showed synergistic inhibitory activities not only on C. albicans yeast and hyphae, but also on biofilms formed from single- and mixed-species and at reduced doses. The combined terpenoids also showed biofilm-penetration capability. The aforementioned terpenoid combination will not only be useful in the treatment of different resistant Candida forms, but also in the safe prevention of biofilm formation.