Agitated Mass Cultivation of Naegleria fowleri

Large quantities (3 X 109 amebae/liter) of Naegleria fowleri were obtained in agitated cultures using a complex medium. Logarithmic growth occurred during the initial 36 hr and the mean generation time was 5.5 hr. The maximum cell yield was 3 X 108 amebae/ml. The pH of the medium increased during logarithmic and stationary growth and the pH optimum for growth initiation in agitated cultures was 5.5, and 6.5 in unagitated cultures. Oxygen tension decreased from 100% to 78% of saturation and amebae did not grow in a 90% N2, 10% CO2, oxygen-free atmosphere. Assays of the culture medium showed little utilization of glucose or other carbohydrates. These data suggest that N. fowleri has a predominantly aerobic metabolism and that it utilizes noncarbohydrate substrates as carbon and energy sources. Naegleria fowleri is an ameboflagellate which may undergo spontaneous cellular differentiation during stationary growth phase (Carter, 1970). It causes fatal amebic meningoencephalitis in humans (Carter, 1972; Duma et al., 1971). To date no definitive studies have been reported concerning its axenic cultural characteristics or physiology although such studies deal with related amebae (Fulton, 1970; O'Dell and Brent, 1974). However, several axenic media have been reported (Cerva, 1969; Chang, 1974; Wong et al., 1975). Naegleria fowleri has been difficult to obtain in sufficient quantities for biochemical analyses. In this study we describe growth conditions which support consistent and maximum yields of N. fowleri during agitated axenic mass cultivation.