Acanthamoeba spp.

MICROBIOLOGY

• Eight species of this free-living, unicellular protozoa are known to infect humans: A. castellanii, A. polyphaga, A. culbertsoni, A. hatchetti, A. rhysodes, A. lugdunensis, A. quina, A griffini.[14]
• Acanthmoeba spp are ubiquitous in nature and can be isolated from air, soil, fresh water, salt water, chlorinated swimming pools, sewage, and heating and ventilation systems.[3]
• A two-stage life cycle includes cysts and trophozoites. Both forms can enter the body. Trophozoites are infectious.
  • Trophozoites actively feed and divide, are pleomorphic, without flagella, and are 14-40 μm in diameter. They have acanthopodia, which are structures responsible for feeding and cell movement.[5]
  • Cysts are dormant, double-walled, are 10-25 μm in diameter, and resistant to chlorine, low temperature, antibiotics, and pH extremes.
    • Three groups (I, II, III) of Acanthamoeba spp. are identified by cyst morphology.
    • Encystation occurs under environmental stresses, i.e., food deprivation, desiccation, or changes in temperature.
• Transmission by inhalation is followed by hematogenous spread. Direct inoculation of skin or eye may cause infection. Nasal rinsing with unsterile tap water is a putative transmission route.[4]
• Described as “Trojan horses” as they can harbor intracellular bacteria, referred to as endosymbionts, which benefit by increased survival or enhanced pathogenicity from interacting with Acanthamoeba.[10]