An experimental study of the infection of oral mucosa in vitro by candida.

Abstract

A sequential study of the invasion of oral mucosa by C. albicans is difficult to accomplish in human beings or in animal models. An in vitro model of oral candidal infection has therefore been established and evaluated by light and electron microscopy. In the model system cultured oral mucosa from neonatal rats and rabbits was infected with C. albicans. The pattern of invasion of the tissues was similar to that reported in vivo although invasion tended to be more extensive and progressed to the underlying connective tissues. The system was evaluated by comparing the invasion of keratinized and non-keratinized epithelium by a number of Candida species; their ability to invade oral mucosa was in accord with their differing pathogenicities, and the extent of invasion of the epithelium by the less pathogenic species was related to its degree of keratinization. The ultrastructural relationship between the superficial epithelium and the fungi was similar to that seen in human oral candidosis, thus validating the model as one in which to study the invasion of epithelium by C. albicans. In examining the fine structure of the invading fungi changes were observed in the organization of the fungal cell wall during the invasive process. Cytochemical localization of acid phosphatase and phospholipase demonstrated that these enzymes are located on the surface of Candida within the tissues although their role in epithelial cell membrane penetration was not clearly established. It is suggested that both fungal enzymes and mechanical force may facilitate fungal invasion. The deep candidal invasion seen in culture did not result from changes within the epithelium but probably reflected the lack of systemic factors. ' An evaluation of the role of immune and non-immune serum factors in the model system indicated that these factors alone may not restrict candidal penetration in vivo.