Pathogenic and Opportunistic Free-Living Amoebae

Acanthamoeba spp., Balamuthia mandrillaris and Naegleria fowleri are free-living amoebae inhabiting a wide variety of environmental niches worldwide, with the potential to cause infections in both humans and animals.

Acanthamoeba spp. and B. mandrillaris are opportunistic pathogens of the central nervous system, lungs, sinuses and skin, primarily in immunocompromised patients and, in severe cases, lead to the fatal disease granulomatous amebic encephalitis.1-3 Among individuals wearing contact lenses, Acanthamoeba spp. is the causative agent of the sight-threatening infection Acanthamoeba keratitis.3 In contrast, N. fowleri, commonly known as the “brain-eating amoeba”, is pathogenic in healthy humans, causing acute and fulminant primary amoebic meningoencephalitis, a water-borne disease of the central nervous system resulting in extensive tissue damage, inflammation and hemorrhagic necrosis.4 Infection with N. fowleri is primarily associated with recreational activities in freshwater lakes and reservoirs naturally heated by the sun, as well as in geothermal sources and water thermally polluted by industry.3,4

The availability of clinical isolates is essential for the advancement of research into the biology, mechanisms of pathogenesis, immunology, antimicrobial susceptibility and molecular characteristics of these amoebae. BEI Resources maintains a collection of free-living amoeba, currently totaling 50 isolates, deposited by the Free-Living & Intestinal Amebas Laboratory, Division of Foodborne, Waterborne, and Environmental Diseases, Centers for Disease Control and Prevention. Each isolate is cataloged with the geographical location, year and source of isolation and reported genotype. Please visit the BEI Resources website for a complete list of isolates in our free-living amoeba catalog.


  1. Marciano-Cabral, F. and G. Cabral. ”Acanthamoeba spp. as Agents of Disease in Humans.” Clin. Microbiol. Rev. 16 (2003): 273-307. PubMed: 12692099.
  2. Cope, J. R., et al. “The Epidemiology and Clinical Features of Balamuthia mandrillaris Disease in the United States, 1974-2016.” Clin. Infect. Dis. 68 (2019): 1815-1822. PubMed: 30239654.
  3. Visvesvara, G. S. “Amebic Meningoencephalitides and Keratitis: Challenges in Diagnosis and Treatment.” Curr. Opin. Infect. Dis. 23 (2010): 590-594. PubMed: 20802332.
  4. Siddiqui, R., et al. “Biology and Pathogenesis of Naegleria fowleri.” Acta Trop. 164 (2016): 375-394. PubMed: 27616699.

Image:  Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri (BEI Resources)

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