In vitro biofilm characterization and activity of antifungal agents alone and in combination against sessile and planktonic clinical Candida albicans isolates

Thirty clinical isolates of Candida albicans were collected from blood or other sterile site infections. Biofilm dry weight and metabolic activity were measured for each isolate. Planktonic and sessile antifungal susceptibilities of each isolate were determined for amphotericin B deoxycholate, caspofungin, and voriconazole. Sessile susceptibilities were determined for the combination of caspofungin/voriconazole. No significant differences in biofilm dry weight or metabolic activity were found between bloodstream and other invasive isolates. Planktonic MIC₉₀ values and sessile MIC₉₀ (SMIC₉₀) values were 0.25 and 2, 0.06 and >256, and 0.5 and 2 μg/mL for amphotericin, voriconazole, and caspofungin, respectively. The SMIC₉₀ of the combination of caspofungin/voriconazole against sessile isolates was 0.5/2 μg/mL. Therefore, the source of invasive C. albicans clinical isolates did not affect in vitro biofilm formation. Susceptibility to antifungal agents decreased when C. albicans was associated with biofilm, and the combination of caspofungin/voriconazole did not appear to provide enhanced activity compared with caspofungin alone.