Investigation of the synergistic effect of clove bud essential oil and micafungin combination against Candida krusei isolates

Objective: Increasing antifungal resistance, particularly the intrinsic fluconazole resistance of Candida krusei, necessitates the enhancement of current therapeutic strategies. This study aimed to investigate the synergistic effect of clove bud essential oil (CBEO) and micafungin (MFG) combination against C. krusei isolates.Methods: Five clinical C. krusei isolates and one reference strain (ATCC 6258) were included in the study. The major component of CBEO was identified by gas chromatography–mass spectrometry (GC-MS) analysis. The antifungal activity of CBEO and MFG was determined using the broth microdilution method. The synergistic activity of the CBEO–MFG combination was evaluated using the checkerboard method.Results: GC-MS analysis determined that the main component of CBEO is eugenol (72.3%), and it also contains minor components such as caryophyllene (12.5%), eugenyl acetate (5.34%), and α-humulene (2.3%). The MIC values of CBEO ranged from 0.004% to 0.06% (v/v), while the MIC values of MFG ranged from 0.002 to 0.03 µg/mL. Synergistic effects were observed in three isolates (50%), additive effects in one isolate (16.7%), and ineffective effects in two isolates (33.3%); no antagonistic effects were detected.Conclusion: The combination of CBEO and MFG demonstrated synergistic activity in a subset of C. krusei isolates. These findings suggest that combining agents with different mechanisms of action may enhance antifungal efficacy and offer a potential approach for combination therapy. In particular, the use of essential oil components alongside antifungal agents may improve treatment effectiveness and provide an alternative strategy for the management of resistant infections. However, further studies are required to validate these findings in clinical settings.