Acanthamoeba is a genus of amoebae found in soil, water, and air, with temporary cytoskeletal projections called pseudopods that allow them to move. They form double-walled cysts and reproduce asexually via binary fission. Although they rarely cause infections, they are known for causing Acanthamoeba keratitis and granulomatous encephalitis in humans. Acanthamoeba keratitis is a painful eye infection associated with contact lens wear, while granulomatous encephalitis is a rare and fatal infection affecting the central nervous system.
An Acanthamoeba is a genus of amoebae found worldwide in soil, water and air. An amoeba is a genus of protozoa, which is a single-celled microorganism belonging to the domain of eukaryotes. Normally, amoebas of this genus contain typical eukaryotic organelles, cytoplasm, and a single nucleus within an outer layer, called the cell membrane. Under a microscope, they appear as a tiny, spiny, oval or round microorganism measuring between ten and thirty-five micrometers in length.
Members of this genus have temporary cytoskeletal projections, called pseudopods or acanthopods, that extend from its cell membranes that allow it to move. These thread-like filaments are composed of actin, which binds to myosin near the cell membrane to cause them to contract, allowing them to move. These small thready projections around the edge of the cell, giving it its characteristic pointed appearance.
The genus Acanthamoeba was discovered by chance by the scientist Aldo Castellani in 1930 when the amoeba contaminated a mushroom culture he was studying. He named the amoeba Hartmannella castellani. Subsequently, as the genus Hartmannella was subdivided into three further categories, or genera: Acanthamoeba, Hartmannella and Glaeseria. The categorization was changed again when scientists made their own family Acanthamoebidae in the 1970s and then placed Hartmannella in another amoeboid family in the 1980s.
One of the distinguishing features of amoebae in this genus is their double-walled cysts. Amoebae form cysts when they encounter harsh conditions by contracting into a ball and secreting a membrane, or two membranes in this case, to protect themselves until conditions become more favourable. The other most distinctive features that members of this genus have are their acanthopodia, which help them move, adhere to surfaces, and capture prey during the vegetative or feeding stages. During this stage, these amoebae are called trophozoites and can feed on algae, bacteria, yeast or other tiny organic substances.
While eating, members of the genus Acanthamoeba grow exponentially during the trophozoite stage to reproduce asexually, via binary fission. In binary fission, the cell doubles in mass and replicates its DNA, or doubles its genetic material. The cell then divides its nucleus, the cell’s brain, into two equal nuclei in a process called mitosis. The large double-nucleus cell then divides into two equal daughter cells via a process known as cytokinesis. Because cell growth and reproduction puts strain on the trophozoite, amoebae often undergo encystment during this time.
Although members of the genus Acanthamoeba occur abundantly in almost all habitats and rarely cause infections, they are best known for their pathogenic qualities. The two human infections most notably caused by Acanthamoeba organisms are Acanthamoeba keratitis and granulomatous encephalitis. Granulomatous encephalitis is a rare and typically fatal infection affecting the central nervous system. It often presents with skin lesions and neurological symptoms and is usually limited to people with compromised immune systems.
Acanthamoeba keratitis is a painful eye infection usually associated with contact lens wear. Several factors contribute to the likelihood of infection, including improper cleaning of contact lenses, wearing contact lenses for excessive periods of time, and exposure to contaminated water. Trophozoites or cysts adhere to lenses, especially worn soft lenses, and then bond to the cornea of the eye. The trophozoites then begin to break down the cells of the eye with phagocytosis, a sort of “eating” process in which the shells of the amoeba count with the help of its acanthopods. This disease is rare and can lead to blindness.
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