Abstract
Whole cell homogenates of Naegleria fowleri were examined by hemolytic and ('51)Cr-release assays for the presence of cytolytic molecules which may participate in the cytopathogenic action of this amoeba. Two distinct cytolytic activities were found. A surface membrane cytolysin was identified which was found to be avidly associated with membranes possessing an equilibrium density of 1.135 g/cm('3) in isopycnic sucrose gradients. The activity of the surface membrane cytolysin was not affected by heating at 75(DEGREES)C for 30 min. The second cytolytic activity was found in putative lysosomes possessing an equilibrium density of 1.162 g/cm('3) and was completely inactivated by heating at 75(DEGREES)C for 30 min. Cytolysis produced in the presence of both cytolysins was consistently synergistic with respect to the activity of either cytolysin alone. The lesions produced on erythrocytes by this cooperative process were characterized by electron microscopy as transmembrane pores resembling a number of other cytolytic effector molecules including the ninth component of complement, perforins of cytolytic T lymphocytes, and the alphatoxin of Staphylococcus aureus.