Comparative studies on related free-living and pathogenic limax amoebae with particular reference to Naegleria.

Abstract

Over two hundred and forty strains of limax amoeba including eight potentially pathogenic strains of Naegleria and Acanthamoeba were isolated from a variety of habitats in South Africa. The amoeboid and flagellate stages of all Naegleria strains examined by light microscopy were found to be similar in morphology. Differences were noted in the excystment of Naegleria fowleri, Naegleria gruberi and other limax amoebae. Time-lapse microcinematography has been utilised to study cytokinesis and motility in the amoeboid and flagellate stages of Naegleria fowleri and Naegleria gruberi. A new phenomenon was observed in Naegleria where amoebae attempted cytokinesis after brief exposure to a temperature of 9°C. The amoeboid and flagellate stages of virulent and avirulent Naegleria were found to be similar in surface topology when examined under the scanning electron microscope. Differences were noted in the excystment patterns of various limax amoebae. No structure suggestive of a surface active lysosome was found in any of the cells examined. A comparative transmission electron microscope study of virulent and avirulent Naegleria and other limax amoebae has revealed striking similarities as well as sharply defined ultrastructural differences. Partioles suggestive of a virus were detected in several of the pathogenic Naegleria. Surface-active lysosomes were not found in any of the amoebae examined. Distinct feeding preferences were evident in Naegleria fowleri and Naegleria gruberi when they were tested on a variety of gram-negative and gram-positive bacteria. Differences were noted on the growth of these amoebae at various temperatures. Cell fractions of Pseudomonas aeruginosa affected excystment, encystment, cell division and the amoeba-to-flagellate transformation in Naegleria. Differences were observed in the transformation kinetics of Naegleria fowleri and Naegleria gruberi at 25ºC and 43º C. A variety of inhibitors affected motility and transformation in Naegleria. For the first time, La[3+]ion, a competitive inhibitor of Ca[2+]ion, was shown to inhibit amoeboid motion, transformation and flagellar beating in Naegleria. Electron microscope observation suggested that La[3+]ion acts on the plasmalemma. Material from two suspected cases of primary amoebic meningoencephalitis was examined and cultured but no limax amoebae were isolated. New criteria for the classification of virulent and avirulent Naeglerid. have been advanced.