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. Here, we assessed the ability of Scedosporium apiospermum 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 [2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide salt] reduction assay. Planktonic cell and biofilm MIC50s were determined as the minimum concentrations that caused ≥50% fungal damage compared to untreated controls. The combined activity of L-AMB (0.5 to 32 mg/liter) and VRC (0.125 to 64 mg/liter) against biofilms was determined by the checkerboard microdilution method and analyzed by the Bliss independence model. Biofilm MIC50s of D-AMB and L-AMB against S. apiospermum isolates were 1 and 2 mg/liter and against FSSC isolates were 0.5 and 1 mg/liter, respectively. Biofilm MIC50s of VRC against S. apiospermum and FSSC were 32 mg/liter and >256 mg/liter, respectively. Synergistic effects were observed at 2 to 4 mg/liter of L-AMB combined with 4 to 16 mg/liter of VRC against S. apiospermum biofilms (mean ΔE ± standard error, 17% ± 3.7%). Antagonistic interactions were found at 0.5 to 4 mg/liter of L-AMB combined with 0.125 to 16 mg/liter of VRC against FSSC isolates, at -28% ± 2%. D-AMB and L-AMB were more efficacious against S. apiospermum and FSSC biofilms than VRC.