This is the first study that investigates the combined antimicrobial effect of fluconazole and fennel oil against Candida species.

This is the first time to investigate the antimicrobial activities of fennel essential oil against biofilm formed by Candida species causing vulvovaginal candidiasis.

Abstract

Aim To screen the antimicrobial activities of some plant essential oils against clinical isolates of C. albicans causing vulvovaginal candidiasis (VVC) and to investigate the antifungal effect of the most active one against planktonic and sessile cells compared to fluconazole.

Methods Screening of biofilm production by C. albicans causing VVC was performed by tissue culture plate method. The antifungal susceptibility of fluconazole was performed by disk diffusion method. Antifungal activities of nine essential oils were screened against strong biofilm-producer, fluconazole-resistant or dose-dependently susceptible clinical isolates and Candida albicans ATCC 10,231 by well diffusion method. Determination of the minimum inhibitory concentration (MIC) of fennel essential oil and fluconazole against planktonic and sessile cells were performed by microdilution methods. Determination of the combined antimicrobial activity of fennel oil and fluconazole was evaluated by checkerboard microdilution assay.

Results From 19 C. albicans strains, 10/19 showed strong ability to form biofilms. None of the tested clinical isolates was sensitive to fluconazole. Fennel oil had significantly higher antifungal activities against tested C. albicans compared with other tested oils (P = 0.000). The MICs of fennel oil for planktonic cells ranged from 0.78% to 6.25% with MIC50 of 3.12% and MIC90 of 6.25%, while concentrations ranging between 6.25% and 25% resulted in 50% biofilm reduction. Synergy or addition between fennel oil and fluconazole were detected against 7/11 strains, while no antagonism was detected.