Anti-biofilm properties of eucalyptol in combination with antifungals against Candida albicans isolates in patients with hematological malignancy

Oral candidiasis is a fungal infection caused mainly by Candida albicans and it is a major problem among hematologic malignancy patients. Biofilm formation is an attributable factor to both virulence and drug resistance of Candida species. The aim of the study was to evaluate the biofilm-producing ability of oral C. albicans isolates and to evaluate the inhibitory activity of eucalyptol on Candida biofilm, alone and in combination with antifungal agents. Samples were collected from the oral cavity of 106 patients with hematologic malignancy. The isolated yeasts were identified by PCR-sequencing. Then C. albicans isolates were analyzed for their biofilm-producing ability by crystal violet staining and MTT assay. The minimum biofilm inhibition concentrations (MBIC) of eucalyptol, amphotericin B, itraconazole, and nystatin and the in vitro interaction of eucalyptol with these drugs were tested according to CLSI-M-27-A3 protocol and checkerboard methods, respectively. From 106 patients, 50 (47.2%) were confirmed for oral candidiasis [mean ± SD age 39 ± 14 years; female 31 (62%) and male 19 (38%)]. C. albicans was isolated from 40 of 50 (80%) patients. From 40 C. albicans isolates, 24 (60%) and 16 (40%) were moderate and weak biofilm producer, respectively. The geometric mean MBIC of amphotericin B, itraconazole, nystatin and eucalyptol were 3.93 µg/mL, 12.55 µg/mL, 0.75 µg/mL and 798 µg/mL, respectively. Eucalyptol interacted synergistically with amphotericin B, itraconazole and nystatin against 12.5, 10, and 22.5% of isolates, respectively. Eucalyptol demonstrated promising activity against biofilm of C. albicans when tested alone or combined with antifungal drugs.