| Candida albicans is the third most common opportunistic fungal pathogen. Treatment of C. albicans infections is hindered in patients with medical implants since the implants provide an adequate substratum for biofilm formation. Biofilms are less susceptible to conventional eradication treatments, such as antimicrobials, and can represent a continuous source of infection as cells detach. Most studies have focused on mature biofilms, thus little is known about the changes that primary adhesion induces in cells. The goal of this study was to determine if adhesion of C. albicans cells to a surface induces the expression of genes that lower their susceptibility to Fluconazole (FCZ).; The hypothesis tested was that contact with a surface and/or the particular environment to which adhered cells are exposed signals the expression of genes that contribute to the decrease in FCZ susceptibility of C. albicans biofilms. The genes encoding for three transport proteins ( CaMDR1, CDR1, and CDR2) were examined using null mutants and promoter fusions to the reporter gene yEGFP. The susceptibility to FCZ and the expression of transport proteins of planktonic cells, cells at the onset of biofilm formation (primary adhered), biofilms, biofilm daughter cells, and detached cells were studied using flow cytometry. The adhesion substratum was medical-grade silicone disks.; Primary adhered mutant cells, deficient in efflux pumps expression, exhibited a higher sensitivity to FCZ than primary adhered wild type (WT) cells (CaI4). The sensitivity to FCZ of Deltacamdr1 and Deltacdr1 null mutants was 10 fold to 100 fold higher, respectively, than that seen in the CaI4. In addition, expression from the CaMDR1 and CDR1 promoters was 2 fold and 5 fold higher, respectively, in primary adhered than in planktonic cells. The results indicated that the difference in resistance seen between planktonic and adhered cells might be a consequence of surface-induced gene expression. We concluded that CaMdr1p and Cdr1p are crucial for the increased resistance to FCZ of primary adhered cells of C. albicans. These findings are vital to understand how adhered cells develop significant resistance to antimicrobial agents and assist in the development of more effective ways to control their growth. |
