Aims: The aim of this study was to attempt to evaluate the antifungal activity of carvacrol in combination with fluconazole or amphotericin B against Candida albicans. Methodology and results: Antifungal susceptibilities to carvacrol alone and in combination with fluconazole or amphotericin B were performed using the CLSI standard reference method against clinical isolates of C. albicans isolated from the immuno-compromised patients. Proteinase production assay and the expression of genes associated with secreted aspartyl proteinases synthesis (SAP1 and SAP2) were carried out to evaluate the antifungal activity of carvacrol in combination with fluconazole or amphotericin B against C. albicans. The carvacrol alone and in combination with fluconazole and amphotericin B exhibited strong inhibitory activity. The carvacrol, exhibited significant synergy and bpartial synergy with fluconazole or amphotericin B against the test isolates. The data indicated that combination of carvacrol with fluconazole or amphotericin B exerted antifungal effects through reducing SAP enzyme activity. The expression levels of SAP1 and SAP2 genes were down-regulated by carvacrol, fluconazole and amphotericin B alone. After carvacrol was employed in combination with fluconazole or amphotericin B, the expression levels of SAP1 and SAP2 genes demonstrated the lower expression in comparison to carvacrol alone. Conclusion, significance and impact of study These results provide proof of concept for the implementation of carvacrol alone or in combination with fluconazole or amphotericin B inhibitors of C. albicans.

One of the main factors for virulence of fungus such as Candida albicans is the ability to change its morphology from yeast to hyphae. Allicin, one of the volatile sulfur-oil compounds from freshly crushed garlic, has a variety of antifungal activities. In this study, the effect of allicin on growth and hyphae production in C. albicans as compared to fluconazole, an antifungal drug was investigated using survival time in vitro and microscopic image at different time intervals. Additionally, the expression of selected genes involved in hyphae formation and development such as SIR2 and SAP1-4 was evaluated by semi-quantitative RTPCR and relative real time RT-PCR. Allicin was shown to down-regulate the expression of SIR2 (5.54 fold), similar to fluconazole (3.48 fold) at 2x MIC concentrations. Interestingly, allicin had no effect on SAPs1-4 expression, whereas fluconazole was able to suppress SAP4 expression. Our findings showed that allicin was effective in suppressing hyphae development of C. albicans to an extent that is sometimes equal or more than fluconazole. Moreover, allicin and fluconazole seemed to share a common anti-Candida mechanism through inhibition of SIR2 gene, while fluconazole appeared to also exert its fungistatic effect through another pathway that involved SAP4 suppression.