Inhibitory Effect of Fluconazole Combined with Amphotericin B on Fluconazole-Resistant Candida albicans Biofilm Formation

 Background & Objective:  The incidence of biofilm-related infections caused by Candida albicans has increased dramatically. C. albicans biofilm-related infections are more resistant to antifungal medications. This work was an attempt to examine inhibitory effects of fluconazole in combination with amphotericin B on fluconazole-resistant C. albicans biofilm.  Materials & Methods:  Fluconazole-resistant C. albicans was identified among colonized clinical isolates of C. albicans obtained from the patients at Shahid Beheshti Hospital, Yasooj, Iran, between September 2016 and January 2017. The MICs of fluconazole alone and in combination with amphotericin B were determined on fluconazole-resistant C. albicans by broth microdilution method based on the CLSI document M27-A3 and the synergistic effects were interpreted by the FIC index. To address the inhibitory effects of drug combinations, we investigated the anti-biofilm activities of fluconazole alone and in combination with amphotericin B against fluconazole-resistant C. albicans using crystal violet staining, light field microscopy and expression analysis of HWP1 using RT-PCR. Results:  Ten percent of the colonizing clinical isolates of C. albicans were found to be fluconazole-resistant. The fluconazole combined with amphotericin B exhibited synergistic and partial synergistic effects against fluconazole-resistant C. albicans isolates with FIC index ranging from 0.50 to 0.75. Our findings demonstrated that fluconazole combined with amphotericin B exerted a significant reduction and inhibition on biomass, biofilm formation and the expression levels of HWP1 (P<0.05). Conclusion:  Fluconazole combined with amphotericin B showed potent inhibitory activity against fluconazole-resistant C. albicans biofilm formation. Other measures are important to determine the effectiveness of the drug combinations against C. albicans biofilm.