Susceptibility to caspofungin and fluconazole and Als1/Als3 gene expression in biofilm and dispersal cells of Candida albicans.

The biofilm of Candida albicans has been implicated as a source of bloodstream infections. Dispersal cells, as the final biofilm stage, are responsible for its spread. The aim of this study was to compare the susceptibility of biofilm and dispersal cells vs. planktonic cells (overnight liquid culture) of C. albicans to caspofungin (CAS) and fluconazole (FLU) when the drugs were added: i) at the beginning of the experiment; ii) after 1.5 h (adherence stage); iii) after 24 h (early mature biofilm). The findings were evaluated after 48 h (mature biofilm) using the XTT reduction assay. Later administration of the drug increased biofilm sessile minimal inhibitory concentration (SMIC(80)) of both FLU and CAS from 1 μg mL(-1) to over 64 μg mL(-1) and from 0.125 μg mL(-1) to over 16 μg mL(-1), respectively. Susceptibility of dispersal cells also decreased with time of administration. We also determined the expression of the Als1 and Als3 genes in 48-h sessile biofilm and dispersal cells of C. albicans SC5314 and compared it to planktonic cells. The expression was normalised to the standard Act1 gene in every condition tested. Quantitative real-time PCR revealed a strong up-regulation of the Als1 gene in the dispersal cells but not in biofilm and high expression of the Als3 gene in both biofilm and dispersal cells. High expression of both Als1 and Als3 genes supports the hypothesis that dispersal cells pose a high-risk of infection.