F-028. Aggregates of Cells Exfoliated from Candida albicans Biofilms Bind to Human Buccal Epithelial Cells by a Mechanism Involving Mannan

E. Hendrix, S. Donahue, S. Durham, R. E. Garner;
Mercer Univ. Sch. of Med., Macon, GA.

Candida albicans resides as a commensal organism in the mucosal tissues of humans. The possible role of the Candida biofilm phenotype in mucosal colonization is currently unknown. Biofilm cells are imbedded in a matrix that forms a barrier around the cells. This biofilm matrix is known to contain primarily polysaccharides and protein and has been shown to restrict antibiotic effectiveness. We hypothesized that matrix-associated substances may also influence microbe/host cell interaction. By affixing monolayers of pooled human buccal epithelial cells to microscope slides, we examined the binding of exfoliated biofilm aggregates to the monolayers in vitro. Biofilm aggregates were obtained from 48 hr biofilms grown on polystyrene with RPMI + MOPS media. Mechanically exfoliated aggregates were stained with the vital fluorescent probe, Fun-1. Polysaccharides within the matrix were counter-stained with calcofluor white. Photomicrograph evaluation suggest that the matrix is involved in aggregate binding to epithelial cells. Sixty percent of the epithelial cells bound some form of the exfoliated biofilm aggregates. Mannan and mannose sugars were used to block aggregate binding. By using a scoring system that accounts for aggregates size, those containing greater than 5 cells (large aggregates) or less than 5 cells (small aggregates), we observed that large aggregate binding was reduced from 40% to 27% by pre-incubation of the epithelial cells with 100 ug/ml Candida mannan. Binding of small aggregates to epithelial cells was reduced from 20% to 15%. The blockade effect of mannan on large aggregate binding was more dramatic than the blockade effect of alpha-methyl mannoside or mannose. We conclude that C. albicans biofilm aggregates exfoliated from in vitro biofilms are fully capable of binding to mucosal epithelial cells without transition to the planktonic phenotype and that this binding may be mediated in part by mannan.