Enhancement of secretory aspartyl protease production in biofilms of Candida albicans exposed to sub-inhibitory concentrations of fluconazole.

The production of Secretory Aspartyl Proteases (Sap) is an important virulence factor of Candida albicans. Many studies have shown that a challenge with sub-inhibitory concentrations of antifungals lead species of Candida to the secretion of higher concentrations of Sap. Nevertheless, published studies only reported the secretion of such enzymes by cells growing in planktonic phase, with few mention of biofilms. The present study evaluated the alterations in the secretion of Sap by C. albicans grown in biofilms and exposed to sub-inhibitory concentrations of fluconazole. The MICs for fluconazole of seven clinical strains were determined for planktonic cells. Biofilm and planktonic cells were grown in the presence of ½ MIC, ¼ MIC, and no medication (control). The relative metabolic activity, indirectly related to cell loads, were estimated by the absorbance of reduced XTT and the Sap activity was evaluated by bovine albumin test. It was observed that 72 h-old biofilms under the influence of ½ MIC had fewer cells than ¼ MIC and control. The production of Sap was inversely proportional to the cell content, with higher secretion in ½ MIC, followed by ¼ MIC and control. Biofilms of C. albicans challenged by sub-MICs of fluconazole tend to secrete higher quantities of Sap.