In vitro penetration of human corneal epithelium by Acanthamoeba castellanii: a scanning and transmission electron microscopy study.

Human corneal buttons were exposed to Acanthamoeba castellanii trophozoites and cysts for 12 hours at 35 degrees C. The buttons examined by light microscopy and scanning and transmission electron microscopy had severe epithelial ulceration and penetration by trophozoites. Observations on trophozoites below the surface suggest that penetration is accomplished by both secreted cytolytic enzymes and phagocytosis. It is likely that the secretion of one or more enzymes constitutes the initial step in preparing the host tissue for endocytosis or that the secretory mechanism is used by the amebas to move through the outer squamous layer to the basement epithelium where phagocytosis occurs. Based on this study and a previous study, it appears that entry into the cornea is a two-step process involving adherence and penetration by trophozoites.