A 30-year-old female stores her contact lenses in tap water. She notices deterioration of vision and visits an ophthalmologist, who diagnoses her with severe retinitis. Culture of the water as well as vitreous fluid would most likely reveal which of the following?

Acanthamoeba is a free-living ameba, as is Naegleria. Naegleria usually causes severe, often fatal, meningoencephalitis, while Acanthamoeba is isolated from contact lens fluid and patients with retinitis who do not store their lenses under sterile conditions. Entry of Acanthamoeba into the CNS can occur from skin ulcers or traumatic penetration. Diagnosis is by examination of the CNS, which contains trophozoites and RBCs but no bacteria. Naegleria, also a free-living amoeba, produces an explosive, rapid brain infection. Babesia are widespread animal parasites, transmitted by ticks. Entamoeba coli is ingested and invade the intestinal epithelium. Pneumocystis jiroveci (not Pcarinii) causes pneumonia in immunocompromised patients. This agent may be an obligate member of the normal flora.