Acanthamoeba

Acanthamoeba is a genus of free-living amoebas capable of causing infection in humans, including encephalitis, keratitis and pneumonia.

One nasty (but rare) disease acanthamoeba is associated with is keratitis of the cornea, in which the clear outside layer of the eye becomes invaded by the organism. This is nearly always associated with contact lens use.

Acanthamoeba species are often present in rivers, sea water, and even water from the tap. It is harmless to humans if swallowed or with normal contact, however it can survive and reproduce in the space between the contact lens and the eye.

For this reason, contact lenses should be washed with specially purchased saline, and deproteinised well. They should not be worn while swimming or surfing.

To culture acanthamoeba in a laboratory, a plain agar plate, with a layer (a lawn) of E. coli is made. Part of the contact lens is placed on the agar plate. If acanthamoeba is present, it will ingest the bacteria leaving a clear patch on the plate around the area of the lens.