Isolation, Identification, and Biological Characterization of Acanthamoeba Polyphaga from a Human Eye

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  • Parasitology Division, Center for Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, Department of Ophthalmology, Baylor College of Medicine, Texas Medical Center, Atlanta, Georgia 30333

Trophozoites and cysts of an Acanthamoeba were repeatedly isolated from the corneal scrapings of a patient suffering from acute ulceration of the right eye. The ameba was cloned and cultivated axenically in a proteose peptone-yeast extract-glucose medium. At a later date the organism was identified as A. polyphaga on the basis of its morphologic characteristics, especially those of cysts. Experimental studies on the in vitro interactions of this organism with monkey kidney tissue culture (Vero line) and its pathogenicity to mice indicated that it was a low virulent strain. When large numbers of amebae (25,000+) were inoculated into Vero cell cultures, cytopathic effects (CPE) were noticed within 5 to 6 days. The CPE consisted of cell shrinkage, nuclear pycnosis, and discontinuity of cell sheet, and the cell culture was totally destroyed in 8 to 10 days. When 20,000+ amebae were instilled intranasally into each of 20 2-week-old mice, only 1 mouse died, on the 28th day. Amebae were isolated from the brain of the dead mouse, and trophozoites and cysts were also demonstrated in the brain sections. When amebae isolated from the brain were intranasally instilled into mice, they failed to kill the mice for at least 1 month; however, when 10,000+ amebae were inoculated intracerebrally, the mice died within 5 to 8 days, exhibiting symptoms of primary meningoencephalitis.