Measuring susceptibility of Candida albicans biofilms towards antifungal agents

Biofilm drug resistance may explain the persistence of many infections in the face of appropriate antimicrobial therapy. Sixty four isolates of planktonic Candida albicans revealed high incidence of resistance to azoles than polyenes antifungal agents. A semiquantitative assay was used to measure the metabolic activity of C. albicans biofilms treated with the antifungal agents and then determine the sessile minimum inhibitory concentration of the antifungal agents which caused 50 % inhibition of the formed biofilms (SMIC50). There was dramatically increase in antifungal concentrations required to kill C. albicans isolates in the sessile forms compared to planktonic forms. Kinetics of biofilm formation showed that the biofilms were highly metabolically active after the first 12 hours. A severe drop in the finally formed biofilms was obtained by adding nystatin at a concentration equal to sub MIC of planktonic cells. On exposure of the biofilms during their formation to nystatin at a concentration equal to sub SMIC50 of formed biofilm cells after 3 and 6 hours, there was a severe drop in the finally formed biofilms. Adding nystatin after 12 and 24 hours, the formed biofilms became more metabolically active. Scanning electron microscope (SEM) revealed that the fully mature biofilm was produced after incubation for up to 48 hour. Growing the biofilm from the beginning with nystatin at SMIC50 resulted in a large reduction in cell numbers and in the thickness of the biofilm compared to the normal biofilm.