Activity of Amphotericin B Formulations and Voriconazole, alone or in combination, against Biofilms of Scedosporium and Fusarium spp

Scedosporium and Fusarium species are emerging opportunistic pathogens, causing invasive fungal diseases in humans, particularly in immunocompromised patients. Biofilm-related infections are associated with increased morbidity and mortality. We herein assessed the ability of Scedosporium apiospermum (SA) and Fusarium solani species complex (FSSC) isolates to form biofilms and evaluated the efficacy of deoxycholate amphotericin B (D-AMB), liposomal amphotericin B (L-AMB) and voriconazole (VRC), alone or in combination, against mature biofilms. Biofilm formation was assessed by safranin staining and spectrophotometric measurement of optical density. Planktonic and biofilm damage was assessed by XTT reduction assay. Planktonic cell and biofilm MIC50's were determined as the minimum concentrations that caused ≥50% fungal damage compared to untreated controls. The combined activity of L-AMB (0.5-32 mg/L) with VRC (0.125-64 mg/L) against biofilms was determined by the checkerboard microdilution method and analyzed by the Bliss independence model. Biofilm MIC50's of D-AMB and L-AMB against SA isolates were 1 and 2 mg/L and against FSSC isolates were 0.5 and 1 mg/L, respectively. Biofilm MIC50's of VRC against SA and FSSC were 32 mg/L and >256 mg/L, respectively. Synergistic effects were observed at 2-4 mg/L of L-AMB combined with 4-16 mg/L of VRC against SA biofilms (mean ΔE±standard error: 17% ± 3.7%). Antagonistic interactions were found at 0.5-4 mg/L of L-AMB combined with 0.125-16 mg/L of VRC against FSSC isolates with -28% ± 2%. D-AMB and L-AMB were more efficacious against SA and FSSC biofilms than VRC.