Acanthamoeba aggregate and encyst on silicone hydrogel contact lenses

Abstract

Purpose : Acanthamoeba keratitis is a serious corneal infection associated with contact lens usage and contaminated water contact. No studies have shown the potential for contact lenses to play a role beyond vector in this infection. Here, we investigated clinical strains of Acanthamoeba using different contact lens materials to draw conclusions on how the interaction of Acanthamoeba with contact lenses may contribute to risk.

Methods : Acanthamoeba trophozoites from strains of T3, T4, and T5 genotypes were inoculated on six silicone hydrogel contact lenses (lehfilcon A, lotrafilcon B, comfilcon A, senofilcon A, samfilcon A, and fanfilcon A) and allowed to adhere. Time-lapse videos were created for up to three days to observe cell behavior on contact lenses and determine cell size and count. Acanthamoeba spheroids were analyzed using confocal microscopy to determine trophozoite and cyst subpopulations over time. Finally, Acanthamoeba spheroids’ disinfection resistance on lenses was compared to individual trophozoites using multipurpose solutions.

Results : Particle count and size were examined: lower count and higher size indicating more aggregation as trophozoites join in a cluster. For all strains, all lens materials tested demonstrated a significantly lower Acanthamoeba particle count than lehfilcon A and lotrafilcon B (p<0.05) from timepoints 2 hours to 12 hours. Similarly, all lens materials demonstrated a significantly higher Acanthamoeba particle size than lehfilcon A and lotrafilcon B from 3 hours through 72 hours (p<0.05). Overall, this demonstrated that the lehfilcon A and lotrafilcon B material allowed significantly less aggregation. Confocal microscopy confirmed the presence of cysts at the center of contact lens-induced spheroids. Finally, lenses with spheroids showed higher Acanthamoeba survival rate to disinfection with the three most common biocides compared to lenses with non-aggregating trophozoites.

Conclusions : Our research establishes that many contact lens materials induce Acanthamoeba to aggregate. This aggregation results in rapid encystment. Encystment is a major hindrance to disinfection by multipurpose solutions which are largely ineffective against Acanthamoeba cysts. This aggregation behavior allows Acanthamoeba to resist disinfection by multipurpose solutions on lenses and may decrease the safety margin for contact lens wearers when good contact lens hygiene practices are not followed.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.