S2.4d Combination antifungal effects of eugenol with voriconazole against Candida tropicalis and Candida krusei strains isolated from the genital tract of mares

Abstract S2.4 Veterinary mycology research, September 21, 2022, 3:00 PM - 4:30 PM Objectives The objective of the current study was to investigate the possibility that eugenol synergizes the antifungal effects of voriconazole on genital isolates of Candida krusei and Candida tropicalis from mares. Methods The antifungal activity of eugenol and voriconazole was evaluated using the broth microdilution assay (CLSI- M27-A3). The synergism of eugenol and voriconazole against genital Candida isolates was evaluated by the microdilution checkerboard method. Results Minimum inhibitory concentration (MIC) values for eugenol and voriconazole ranged from 400 to 800 μg/ml and 1 to 8 μg/ml, respectively, for C. tropicalis isolates, and from 200 to 400 μg/ml for eugenol and 2 to 16 μg/ml for voriconazole against C. krusei isolates. Eugenol decreased the arithmetic mean of MIC for voriconazole against C. tropicalis and C. krusei isolates from 2.66 to 0.46 μg/ml and 7.77 to 0.41 μg/ml respectively. The fractional inhibitory concentration index (FICI) values for the eugenol voriconazole combination ranged from 0.25 to 0.88 and 0.19 to 0.63 for C. tropicalis and C. krusei isolates respectively. A synergistic effect of eugenol in combination with voriconazole was observed for 83.3% of C. tropicalis and 77.7% of C. krusei isolates. The antagonistic activity was not seen in any of the isolates tested. Conclusions Eugenol showed fungistatic and fungicidal effects against genital Candida isolates and, in combination, synergized the antifungal effects of voriconazole. The eugenol-voriconazole combination can lay the foundation for a therapeutic approach against isolates in which azole resistance has increased over time.