Mechanisms of Oral Colonisation by Candida albicans

Oral candidosis often affects the very young, the elderly and the immunocompromised. In order to cause an infection, the yeast Candida albicans must first adhere to an oral surface. Understanding C. albicans oral adhesion mechanisms may lead to novel treatments that prevent colonisation and hence preclude candidosis. Objectives: The aim of this study was to characterise C. albicans adhesion to: cultured epithelial cells; denture acrylic; and to voice prosthesis silicone rubber. Methods: Assays were developed to measure the adhesion of radiolabelled C. albicans cells to the three substrates: HEp-2 epithelial cells, denture acrylic and silicone rubber. The effect of adding pooled human saliva to the assays was determined. Proteins from saliva that attached to C. albicans cells, or to adhesion substrates, were analysed by SDS polyacrylamide gel electrophoresis, immunodetection, and N-terminal sequencing. Results: Pooled human saliva increased the attachment of C. albicans cells to cultured HEp-2 cells and to silicone rubber in a dose-dependent fashion. Biotin labelling of saliva proteins, and immunodetection, indicated that free secretory component (SC) from secretory immunoglobulin A (sIgA) bound to C. albicans cells and promoted adherence to HEp-2 cells. Pre-incubation of HEp-2 cells with saliva, however, did not increase C. albicans adherence. In contrast, other salivary proteins were selectively adsorbed to denture acrylic and silicone rubber. One of these proteins, to which C. albicans adhered when the protein was electroblotted onto nitrocellulose, was identified by N-terminal sequencing as parotid salivary protein (PSP). Conclusions: There are distinct mechanisms of C. albicans adhesion to different oral surfaces. Adhesion to epithelial cells is promoted by free SC bound to the yeast cells, whilst adhesion to denture acrylic is promoted by PSP bound to the substrate. This work was supported by the NZ Lottery Grants Board, the NZ Dental Research Foundation and University of Otago Research Grant 0020030854.