The effects of tea polyphenols on Candida albicans: inhibition of biofilm formation and proteasome inactivation.

The adherence of Candida albicans to one another and to various host and biomaterial surfaces is an important prerequisite for the colonization and pathogenesis of this organism. Cells in established biofilms exhibit different phenotypic traits and are inordinately resistant to antimicrobial agents. Recent studies have shown that black and green tea polyphenols exhibit both antimicrobial and strong cancer-preventive properties. Experiments were conducted to determine the effects of these polyphenols on C. albicans. Standard growth curves demonstrated a 40% reduction in the growth rate constant (K) with a 2 mg/mL concentration of Polyphenon 60, a green tea extract containing a mixture of polyphenolic compounds. Cultures treated with 1.0 micromol/L -(-)epigallocatechin-3-gallate (EGCG), the most abundant polyphenol, displayed a 75% reduction of viable cells during biofilm formation. Established biofilms treated with EGCG were also reduced, by 80%, as determined through XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) colorimetric assays. Identical concentrations of epigallocatechin and epicatechin-3-gallate demonstrated similar biofilm inhibition. Further investigations regarding the possible mechanism of polyphenol action indicate that in vivo proteasome activity was significantly decreased when catechin-treated yeast cells were incubated with a fluorogenic peptide substrate that measured proteasomal chymotrypsin-like and peptidyl-glutamyl peptide-hydrolyzing activities. Impairment of proteasomal activity by tea polyphenols contributes to cellular metabolic and structural disruptions that expedite the inhibition of biofilm formation and maintenance by C. albicans.