[Ultrastructure study of pathogen of acanthamoeba keratitis]

To observe the ultrastructure of the strains of acanthamoeba isolated from acanthamoeba keratitis (AK), the morphologic changes of acanthamoeba after culture with 0.02% chlorhexidine, and ultrastructure characteristics of acanthamoeba in corneal tissue of AK.

It was a experimental study. The ultrastructure of acanthamoeba strains cultured with 0.02% chlorhexidine was observed with scanning electron microscope (SEM). The excited cornea tissues from AK were observed with transmission electron microscope (TEM).

Cultured acanthamoeba trophozoites were approximately 15 - 45 microm in diameter, appeared irregularly round or oval in shape, with rough surface and intrusion of cytoplasm. The trophozoite propagated by ways of binary division. The acanthamoeba cysts were approximately 10 - 25 microm in diameter, round in shape and with a plica-like surface. The acanthamoeba could change from trophozoite to cyst. The amoeba emerging through ostioles could turn into trophozoite and left an empty cyst. After cultured with 0.02% chlorhexidine for 24 hours, the trophozoite and cyst collapsed and distorted. However, after clinical treatment with 0.02% chlorhexidine, only the cysts could be seen in corneal tissue of AK. Ecto-and endo-cystic walls were preserved, but the cytoplasma was aggregated and the sub-cytoarchitecture were degenerated or disappeared. DISCUSSION Chlorhexidine at a concentration of 0.02% kills acanthamoeba trophozoites and cysts in vitro. Chlorhexidine (0.02%) also kills trophozoites and inhibits the activity of cysts in corneal tissues. However, it should be noticed that the inactive cysts can stay in the cornea for a long time and may cause an immuno-pathologic inflammation of the cornea.