A Fluorometric Assay for the In Vitro Evaluation of Activity against Naegleria fowleri Cysts

Primary amoebic meningoencephalitis (PAM) is a lethal and rapid infection that affects the central nervous system and is caused by the free-living amoeba Naegleria fowleri. The life cycle of this protozoa consists of three different stages: The trophozoite, flagellate and cyst stages. Currently, no fully effective molecules have been found to treat PAM. In the search of new antiamoebic molecules, most of the efforts have focused on the trophozoidal activity of the compounds. However, there are no reports on the effect of the compounds on the N. fowleri cyst viability. In the present study, the cysticidal activity of four different molecules was evaluated using an alamarBlue based fluorometric assay. All the tested compounds were active against the cyst stage of N. fowleri. In fact, all the molecules except the amphotericin B, showed highest activity toward the cyst stage than the trophozoite stage. This work could be an effective protocol to select molecules with cysticidal and trophozoidal activity that can be considered a future PAM treatment. IMPORTANCE In the search of new anti-Naegleria fowleri compounds, most of the works focus on the activity of different molecules against the trophozoite stage; however, none of them include the effect of those compounds on the cyst viability. This manuscript presents a solid and reliable assay to evaluate the activity of compounds against the cyst stage of N. fowleri.