Time-Lapse Tracking of Acanthamoeba castellanii Trophozoite Activity During Exposure to Contact Lens Disinfectants

To compare the immediate response of Acanthamoeba castellanii trophozoites to the sudden exposure of common contact lens disinfectants by tracking movement behavior through time-lapse imaging. We cultured Acanthamoeba trophozoites and imaged them under brightfield microscopy. We introduced disinfectants at commercially relevant concentrations into the environment of the trophozoites for 30 minutes. After exposure, we neutralized the disinfectants and returned the samples to a growth medium for incubation. We converted recordings into binary image sequences and analyzed trophozoite movement and body morphology using cell-tracking software. After placing amoebae in a growth medium, we assessed recovery at 1 day and 3 days post-exposure. Exposure to 0.05% w/v povidone-iodine (PVP-I) resulted in complete cessation of trophozoite movement within 2 minutes, whereas 3% v/v hydrogen peroxide (H2O2) required nearly 4 minutes to halt activity. H2O2 exposure also induced a morphological transformation into rounded forms. PVP-I did not trigger this morphological change. Exposure to 0.0001% w/v polyhexamethylene biguanide (PHMB) only partially reduced movement speed during the 30-minute exposure. We observed no trophozoite recovery in PVP-I-exposed samples following reintroduction to the growth medium, whereas recovery occurred in H2O2- and PHMB-treated samples. Compared with H2O2 and PHMB, PVP-I rapidly immobilized Acanthamoeba trophozoites and prevented recovery. This suggests that PVP-I in the environment may be immediately far less tolerable to Acanthamoeba than other disinfecting agents and offers a novel rationale for its high disinfecting efficacy.