In Vitro Contribution of Herbal Products on the Activity of Antifungal Drugs against Clinical Candida Isolates

Aims: The contribution of natural compounds may provide significant progress in the discovery of new antifungal drugs. We aimed to investigate the contribution of carvacrol, farnesol, epigallocatechin gallate, ginger, naringenin and curcumin on the activity of antifungals, voriconazole, caspofungin and amphotericin B against clinical Candida isolates.

Methodology: Eight clinical Candida isolates were included in this study. The MIC values of each herbal compound and each antifungal were determined using the reference broth microdilution method. The interactions of herbal compounds and antifungal drugs were assessed by checkerboard microdilution method.

Results: The MIC values ranged from 60 to 160 μg/mL for carvacrol, from 16 to 64 μg/mL for epigallocatechin gallate, from 80 to 320 μg/mL for ginger and 800 μg/mL for curcumin. Any MIC value was not detected for farnesol and naringenin in concentrations tested. Although the most common interaction type was indifference, farnesol, carvacrol and ginger reduced the MICs of all three antifungals against most isolates. Voriconazole and amphotericin B MICs decreased in combinations with epigallocatechin gallate, whereas naringenin and curcumin did not show any conspicuous effect on antifungal drug activities.

Conclusion: We showed that carvacrol, epigallocatechin gallate, curcumin and ginger enhanced the activity of voriconazole, caspofungin and amphotericin B against Candida isolates in vitro. These compounds may represent novel agents to be used in combination with available antifungal drugs to lower the doses of antifungals, thus toxic side effects and treatment costs may decrease.