Candida albicans is a well-armed opportunistic pathogen that produces a diverse array of virulence factors. One recently recognized virulence attribute is the ability to live and persist in a biofilm. Candida biofilm infections are commonly associated with medical devices. Central venous catheter (CVC) related bloodstream infections are among the most important biofilm infections. These infections are extremely difficult to treat without removal of the medical device due to the drug resistance associated with biofilm growth. The mechanisms responsible for biofilm resistance are not well-understood. Our long term goal is to elucidate the mechanisms responsible for drug resistance in Candida biofilms as a prerequisite to the development of therapeutic strategies that can be used to attenuate this disease process. The specific hypothesis behind the proposed research is that 2-glucan molecules produced during C. albicans biofilm growth interact with antifungal drugs and prevent binding to intracellular drug targets. This hypothesis is based on the following observations. First, the biofilm process is associated with cell wall changes that are associated with increased 2-1,3 glucan content. In addition, the composition of the extracellular matrix is predominantly carbohydrate, including 2-glucan. Second, isolated biofilm matrix is capable of binding to the antifungal fluconazole. Furthermore, addition of biofilm matrix and other exogenous sources of 2 -glucan to free floating (planktonic) C. albicans renders the cells resistant to the antifungals, fluconazole and amphotericin B. Also, enzymatic alteration of 2- glucan during biofilm growth enhances the activity of the antifungal drugs. Third, mutation of three genes in the glucan synthesis and modification pathway results in enhanced susceptibility to the antifungal fluconazole. Based on these observations, the experimental focus of this proposal is on the glucan pathway.
The specific aims are designed to (i) define the significance of genes in the glucan synthesis and modification pathways for biofilm formation and drug resistance, (ii) characterize the structure and quantity of the biofilm associated extracellular carbohydrate in parent and mutants in the glucan pathways, and (iii) provide a structural and quantitative evaluation of the biofilm glucan and antifungal drug interaction.
Candida albicans biofilm infection of medical devices is common and causes significant patient mortality. Drug-resistance associated with biofilms is associated with poor outcomes. The mechanisms underlying the resistance phenotype are poorly understood. The current proposal is designed to determine the role of a secreted carbohydrate in biofilm resistance.
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