Cocultivation of the amoeba Naegleria fowleri and the amoebicin- producing strain Bacillus licheniformis M-4.

Antagonism between Bacillus licheniformis M-4 and the pathogenic amoeba Naegleria fowleri HB-1 during cocultivation was influenced by the composition of the medium and the initial amoeba/bacterium ratio. While a ratio of 50 caused complete lysis of amoebae in soil extract with 0.3% glucose (SEG) before 72 h, this ratio had to be at least 12-fold lower in order to obtain similar results in Cline medium. Sporulation of B. licheniformis M-4 took place much earlier in SEG. Amoebicin production was stimulated by the presence of amoebae by either shortening the time of production (as in SEG) or increasing the amount of amoebicins released (as in Cline medium). Electron microscopy showed that amoebae cocultivated in the Cline medium contained bacteria enclosed in digestive vacuoles, while amoebae from SEG cocultures did not.