Cultivation of Pathogenic and Opportunistic Free-Living Amebas

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Abstract
SUMMARY: Free-living amebas are widely distributed in soil and water, particularly members of the generaAcanthamoebaandNaegleria. Since the early 1960s, they have been recognized as opportunistic human pathogens, capable of causing infections of the central nervous system (CNS) in both immunocompetent and immunocompromised hosts.Naegleriais the causal agent of a fulminant CNS condition, primary amebic meningoencephalitis;Acanthamoebais responsible for a more chronic and insidious infection of the CNS termed granulomatous amebic encephalitis, as well as amebic keratitis.Balamuthiasp. has been recognized in the past decade as another ameba implicated in CNS infections. Cultivation of these organisms in vitro provides the basis for a better understanding of the biology of these amebas, as well as an important means of isolating and identifying them from clinical samples.NaegleriaandAcanthamoebacan be cultured axenically in cell-free media or on tissue culture cells as feeder layers and in cultures with bacteria as a food source.Balamuthia, which has yet to be isolated from the environment, will not grow on bacteria. Instead, it requires tissue culture cells as feeder layers or an enriched cell-free medium. The recent identification of another ameba,Sappinia diploidea, suggests that other free-living forms may also be involved as causal agents of human infections.