N. fowleri has three morphological forms:
- A feeding trophozoite stage
- A dormant cyst stage
- A transitional flagellate stage (N. fowleri is the only pathogenic free-living amoeba with a flagellate state)
In the free-living state, the amoeboid trophozoite feeds on bacteria and other organic materials. It reproduces by binary fission. When deprived of nutrients, the trophozoite transforms into a flagellate state. This form is usually pear-shaped with two flagella emerging from the narrow portion. The flagellate form does not divide or feed. It will revert to the amoeboid form when nutrients are restored. When conditions become adverse, such as diminished food supply or colder temperatures, the trophozoite transforms into a resistant cyst stage. It is the trophozoite stage that is infective.
