A 30-year-old female stored her contact lenses in tap water. She noticed deterioration of vision and visited an ophthalmologist who diagnosed her with severe retinitis. Culture of the water as well as vitreous fluid would most likely reveal

Acanthamoeba is a free-living ameba as is Naegleria. Naegleria usually causes severe, often fatal, meningoencephalitis, while Acanthamoeba is uncommonly isolated from contact lens fluid and patients with retinitis who do not store their lenses under sterile conditions. Acanthamoeba can be grown on non-nutrient agar plates using Escherichia coli as a food source. They are identified microscopically with use of a nonspecific fluorescent stain.