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Keywords
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horse, mare, yeast, reproductive candidiasis, eugenol, voriconazole, synergistic activity
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Abstract
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Background: Due to the limited range of antifungals available to treat genital Candida
infections and the emergence of resistant isolates, attention has focused on the antifungal
potency of natural compounds with promising biological properties.
Objectives: To examine whether eugenol synergises the in vitro efficacy of voriconazole
against Candida strains isolated from the genital tract of mares.
Study design: In vitro experiment.
Methods: The antifungal activity of eugenol and voriconazole was evaluated using
the broth microdilution assay (CLSI- M27-A3). 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 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. Antagonistic activity was not seen in any of the isolates tested.
Main limitations: Since in vitro antifungal susceptibility tests are not systematic analyses,
any selection bias could influence the results. In addition, in vitro susceptibility
does not uniformly predict clinical success in vivo.
Conclusions: Eugenol showed fungistatic and fungicidal effects against genital
Candida isolates and, in combination, synergised the antifungal effects of voriconazole.
The eugenol-voriconazole combination can lay the foundation for a ther
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