Some factors stimulating movement by Naegleria fowleri

Naegleria fowleri is a free living ameba which is able to infect the brain of humans and some other mammals. Little is understood about the adaptations and responses to stimuli which occur during infection. To better analyze the microbe's migratory responses to stimuli, factors were studied which influenced in vitro locomotion systems used as models for in vitro migration. Migration could effectively be measured with either polycarbonate or nitrocellulose filter assay methods in dose response experiments to attractants such as whole Escherichia coli C or its cell-free extract using Page's amebae saline but not Hanks balanced salt solution as others have reported. Migration appeared sensitive to the presence of wetting agents in the filters, to pore size, and the pore size for a particular brand of filter. Interestingly, locomotion without attractant was strongly increased in adherent cultures as a function of culture crowding, and absent from log phase suspension culture grown cells. It could be induced by incubation in buffer for two hours or continuing the cultures into stationary phase. This indicated that high and variable rates of locomotion for Naegleria fowleri are not random responses, but are a reproducible response to certain stimuli which can occur during culture or prolonged incubation in buffer. These results suggest that these amebae are not naturally rapidly moving, as might have been thought, but their locomotion is readily increased by crowding and surface contact. These effects would cause the cells to disperse into the tissues from an infection site.