Quantitative Growth of Naegleria in Axenic Culture

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A strain of Naegleria gruberi, isolated from a Vero cell culture and designated TS-1, was axenically cultivated in monolayer and mass aerating suspension culture. Cultural conditions for constant growth parameters and high-exponential cell densities were defined. Serum or other supplemented fractions were found essential in both Trypticase-yeast extract-glucose (TYG) and Casitone (CAS)-based media. Monolayer cultures grown in the CAS medium required lower levels of serum to reach maximum stationary densities of amoebae than cultures grown in the TYG medium. Heat-killed (121 C, 10 min) whole cell and cell lysate bacterial fractions were capable of replacing the serum in both the TYG and CAS media. Heat-killed bacterial fractions provided the same levels of growth as attained with serum in TYG medium, whereas the bacterial lysate supported only minimal growth in the same medium. In the CAS medium, both bacterial fractions resulted in the same level of growth which was equal to that obtained in reduced serum content. Strain TS-1 was established in suspension culture with the CAS medium used in monolayer culture. The addition of sheep red blood cells (RBC) or RBC lysate greatly enhanced growth responses. Further modifications resulted in a final medium for suspension culture consisting of Casitone-yeast extract-glucose-vitamin base, supplemented with serum and RBC lysate. This medium supported growth with a mean generation time of 9 h at 30 C and a stationary phase yield of greater than 5 × 106 amoebae per ml.

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