Candida albicans Ultrastructure: Colonization and Invasion of Oral Epithelium

Abstract

The colonization and invasion of various animal [rat and rabbit] oral mucosae by C. albicans were examined in an organ culture model. Scanning and transmission electron microscopy of the oral epithelium 12-30 h after inoculation with the fungus revealed the morphological relationships between host and parasite. Examination of the fungi in thin sections showed 5 distinct layers in the cell wall of C. albicans within the epithelium, but changes were evident in organization and definition of the outer cell wall layers in budding hyphae and in hyphae participating in colonization and invasion of the epithelial cells. Adherence of the fungus to the superficial cells of the oral mucosa appeared to involve intimate contact between the epithelial cell surface and the deeper layers of the fungal cell wall. During invasion a close seal was maintained between the invading hyphae and the surrounding epithelial cell envelope, there being no other evidence of damage to the host cell surface except at the site of entry. Within the epithelial cells there was only occasional loss of cytoplasmic components in the vicinity of the invading hyphae. Enzymatic lysis associated with the invasive process may be localized, and the mechanical support provided by surface adherence and the intimate association between the fungus and the epithelial cell envelope may permit growth of Candida through the epithelium.