The inhibitory activity of magnolol on Candida tropicalis

Background: Candida tropicalis (C. tropicalis) is isolated third in non- albicans Candida species. Antifungal agents used for the treatment of Candida species are mainly Fluconazole (FLCZ) and amphotericin-B (AMPH-B) and so on. However, according to the SENTRY Antifungal Surveillance Program, it has been reported that the C. tropicalis FLCZ resistance rate is increasing. It is also known that AMPH-B has nephrotoxicity. Magnolol first extracted from traditional Chinese medical plant magnolia officinalis. Previous studies demonstrated that magnolol inhibit the growth of candida species. Nevertheless, there few studies of C. tropicalis on magnolol. In this study, we investigated the activities of magnolol against C. tropicalis. Methods and materials: We used 20 strains of C. tropicalis clinical isolates (C. t 1–20) and C. tropicalis ATCC 750. We investigated MIC (minimum inhibitory concentration), MBIC (minimum biofilm inhibitory concentration), Biofilm formation (BF) ability and Time-kill (TK) assay (6h, 12h, 24h, 48h). MBIC used 3 strains (C. t 1, 4, 9) with different BF ability and was assayed 4 time point (6h, 12h, 24, 48h). Time-kill assay (6h, 12h, 24h, 48h) used C. tropicalis ATCC 750, the magnolol concentration was determined as MIC and sub-MIC concentration. Results: The MIC90 of FLCZ, AMPH-B and magnolol with respect to C. tropicalis were 0.5 μg/mL, 1 μg/mL and 64 μg/mL, respectively. BF ability was produced in all strains on microtiter plate. All antifungal drugs and magnolol against MBIC were >512 ug/mL at all 4 time point. TK assay was inhibited growth for 48 hours at MIC concentrations, but not inhibited growth for 24 hours at concentration sub-MIC. Conclusion: It was suggested in MIC that magnolol exhibits antifungal activity against C. tropicalis. However, magnolol showed no antifungal activity in MBIC like other antifungal agents. These indicate that magnolol may not show antifungal activity after C. tropicalis BF.