Nonpathogenic Free-Living Amoebae

Free-living amoebae (FLA) are unicellular, eukaryotic protozoa found in virtually all soil and aquatic environments (). All FLA are characterized by a feeding and replicating trophozoite form that, in most genera, can produce a resistant cyst stage in response to adverse conditions (). FLA claim our interest not only as fundamentally interesting microbes about which there is still much to be learned, but also because of the capacity for certain species to cause serious and often fatal infections in humans. The amoeboflagellate Naegleria fowleri is found in thermally polluted water and causes primary amoebic meningoencephalitis in previously healthy persons (, , ). Members of the genus Acanthamoeba are among the most common FLA and some species cause granulomatous amoebic encephalitis in the immunocompromised host and a destructive eye infection in previously healthy persons termed Acanthamoeba kerdtitis (, ) (see Note 1).