Pathogenic and Opportunistic Free-Living Amebae

Abstract

Small, free-living amebae belonging to the genera Naegleria, Acanthamoeba, and Balamuthia have been identified as agents of central nervous system (CNS) infections of humans and other animals. The concept that these small, free-living amebae may occur as human pathogens was proposed by Culbertson and colleagues, who isolated Acanthamoeba sp. The genus Acanthamoeba contains as many as 24 species in three groups, with groupings based largely on morphologic characteristics. The chapter talks about clinical significance of Naegleria Meningoencephalitis, Acanthamoeba Encephalitis, Balamuthia (Leptomyxid) Encephalitis, and Acanthamoeba Keratitis. It outlines the recommended procedure for isolating free-living pathogenic amebae from biological specimens. Identification of living organisms to the genus level is based on characteristic patterns of locomotion, morphologic features of the trophozoite and cyst forms, and results of enflagellation experiments. Acanthamoeba spp can easily be cultivated axenically, without the addition of serum or host tissue, in many different types of nutrient media, e.g., proteose peptone-yeast extract-glucose medium, Trypticase soy broth medium, and chemically defined medium. The serologic techniques discussed in this chapter have been developed as research tools and are not routinely available to clinical laboratories. Most clinical laboratories rely on the agar plate technique for the isolation and identification of these small, free-living, and pathogenic amebae, as other techniques, like PCR, are not available and sometimes not even feasible. The laboratories usually send the specimens to an outside laboratory like the Centers for Disease Control (CDC) for identification and interpretation.