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Cultivation of pathogenic and opportunistic free-living amebas
1Viral and Rickettsial Disease Laboratory, State of California Department of Health Services, Richmond, California 94804, USA. fschuste@dhs.ca.gov
Abstract:
Free-living amebas are widely distributed in soil and water, particularly members of the genera Acanthamoeba and NAEGLERIA: 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. Naegleria is the causal agent of a fulminant CNS condition, primary amebic meningoencephalitis; Acanthamoeba is responsible for a more chronic and insidious infection of the CNS termed granulomatous amebic encephalitis, as well as amebic keratitis. Balamuthia sp. 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. Naegleria and Acanthamoeba can 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.
Insights
Free-living amebas like Naegleria and Acanthamoeba can cause serious central nervous system (CNS) infections. Culturing these opportunistic pathogens in vitro is crucial for understanding their biology and diagnosing infections.
Area of Science:
- Medical Microbiology
- Environmental Health
- Parasitology
Background:
- Free-living amebas, notably Acanthamoeba and Naegleria, are prevalent in soil and water.
- These organisms are opportunistic human pathogens causing central nervous system (CNS) infections in various hosts.
- Naegleria causes primary amebic meningoencephalitis, while Acanthamoeba causes granulomatous amebic encephalitis and amebic keratitis.
Purpose of the Study:
- To highlight the significance of in vitro cultivation for studying free-living amebas.
- To emphasize the role of these amebas as human pathogens.
- To discuss the isolation and identification of amebic pathogens from clinical samples.
Main Methods:
- In vitro cultivation of Naegleria and Acanthamoeba using axenic media or tissue culture cells.
- Cultivation of Balamuthia using tissue culture cells or enriched cell-free media, as it does not grow on bacteria.
- Discussion of culturing techniques for isolating and identifying pathogenic amebas.
Main Results:
- In vitro cultivation provides a foundation for understanding ameba biology.
- Culturing is essential for isolating and identifying amebic pathogens from clinical specimens.
- Different ameba species require specific cultivation methods (e.g., Balamuthia requires tissue culture cells).
Conclusions:
- In vitro cultivation is a vital tool for the study and diagnosis of amebic infections.
- Understanding the cultivation requirements of different amebas is key to their successful isolation.
- Emerging amebic pathogens like Balamuthia and Sappinia diploidea warrant further investigation.