Application of flow cytometry to studies of pathogenic free-living amoebae

Species of small, free-living amoebae of the genera Naegleria and Acanthamoeba can cause fatal amoebic meningoencephalitis. Previous investigations have shown that pathogenic amoebae are associated with thermally altered water. Flow cytometric techniques for identifying species of pathogenic and nonpathogenic amoebae from such water have been developed, using immunofluorescence and fluorescein-bound concanavalin A. Flow cytometry is accomplished with a cytofluorograph, in which cells are dispersed in a suspended carrier liquid and passed in front of a focused argon ion laser beam. Cells are then distinguished by the degree of scattered light (size) or fluorescence. Flow cytometry techniques have proven efficient for environmental samples, as indicated by the identification of pathogenic Naegleria fowleri and nonpathogenic Naegleri gruberi and Acanthamoeba castellanii isolated from the Savannah River Plant in South Carolina. Cytofluorographic analysis of environmental samples has several advantages over the current methods of isolation and classification of free-living amoebae. With this system, it is possible to rapidly identify species and quantitate mixtures of pathogenic amoebae in environmental samples. Cytofluorographic analysis of amoebic isolates reduces the time presently required to screen environmental sites for pathogenic amoebae. The cytofluorograph permits detection and species identification of nonthermophilic Naegleria spp. and Acanthamoeba spp. that could not easily be isolated for species identification by conventional methods. Other advantages of flow cytometry over fluorescent microscopy include a high degree of statistical precision due to the large numbers measured, high immunofluorescent titers, and elimination of subjectivity and fluorescence fading.