Candida albicans Ultrastructure: Colonization and Invasion of Oral Epithelium

Abstract

The colonization and invasion of various animal oral mucosae by Candida albicans were examined in an organ culture model. Scanning and transmission electron microscopy of the oral epithelium between 12 and 30 h after inoculation with the fungus revealed the morphological relationships between host and parasite. Examination of the fungi in thin sections showed five distinct layers in the cell wall of C. albicans within the epithelium, but changes were evident in the 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.

A Role of Secreted Proteinase of Candida albicans for the Invasion of Chick Chorio‐Allantoic Membrane

“…Electron microscopic observations of mycotic tissue have shown invading fungi surrounded by electron-lucent areas, which have been interpreted as the result of enzymic lysis of host cells (9,14,16,17,23,24,28). On the contrary, there are many reports claiming that host cellular structures show scarcely any changes in the vicinity of Candida cells (1,3,5,7,15,26). Our electron micrographs showed the two aspects of the tissue disintegration: detachment of tissue cells due to the dissolution of desmosomes and the degeneration of host cells due to phagocytosed yeast cells.…”

Infections and non‐neoplastic diseases of the oral mucosa

“…The process of colonization and invasion of animal mucosa has been examined in an organ culture system by Howlett and Squier (1980). During contact and invasion by fungal cells, a close seal is maintained between the invading hypha and the surrounding epithelial cell envelope, which shows remarkably little evidence of damage except at the site of entry.…”

Candida albicans hyphal invasion: thigmotropism or chemotropism?

“…Hyphal penetration of human oral epithelium appeared independent of surface contours [12]; longitudinal sections of infected cells showed hyphal invasion originating at both the`peaks' and troughs' of the cell surface undulations. A more detailed study on neonatal rodent oral epithelium also reported hyphal penetration sites over the open surface of the cells [13]. These observations show that Candida has a clear ability to act as a directly penetrating pathogen on open surfaces and even on healthy keratinised epithelium.…”

“…Growth would then continue over the open surface until a localised hot spot' of signal is perceived or chemical feedback from exploratory epithelial degradation indicates a suitable penetration site. This could explain hyphal penetration patterns on the ridged surface of rodent oral epithelium [13] where invasion sites were distant from the blastospore. It would be reasonable to expect invasion sites closer to the blastospore if the surface ridges were invasion cues as the hyphae would encounter them almost immediately.…”

“…Such an experimental path would however be directed by the phytopathogen paradigm^hypotheses would centre around measurable contours on the epithelial cell surface which trigger hyphal re-orientation or penetration. For an invasive response, this raises an experimental problem exempli¢ed by an observation made on rodent oral epithelia infected by C. albicans [13]: surface ridges (covering the cell surface) were absent around the hyphal penetration site. It is feasible that the ridges (estimated height from micrographs 6 0.1 Wm) could have been eroded by secreted proteinases, as C. albicans hyphal invasion of epithelium can be prevented by pepstatin [11].…”