Acanthamoeba is a genus of amoebae, one of the most common protozoa in soil, and frequently found in fresh water and other habitats. Acanthamoeba has two evolutive forms, the metabolically active trophozoite and a dormant, stress resistant cyst. Trophozoites are small, usually 15 to 35 µm in length and amoeboid in shape. In nature, Acanthamoeba species are free-living bacterivores, but in certain situations they can cause infections in humans and other animals.