Efficacy of contact lens systems against recent clinical and tap water Acanthamoeba isolates

Purpose: A recent increase in Acanthamoeba keratitis (AK) cases has been associated with Complete MoisturePlus, although many cases used other solutions. Complete MoisturePlus contains taurine and hydroxypropyl methylcellulose, unlike other multipurpose solutions (MPSs). The purpose of this study is to (1) determine contact lens solution efficacy against recent clinical and tap water Acanthamoeaba isolates and (2) determine whether taurine inclusion increases Acanthamoeba survival against contact lens solutions. Methods: Acanthamoeba T4 trophozoites from recent AK clinical and tap water isolates were placed on multiple concentrations of taurine-saline agar for 72 hours with Enterobacter aerogenes as prey. Amoebae were exposed for 6 and 24 hours to hydrogen peroxide solutions and MPSs (ReNu Multiplus, Complete MoisturePlus, AMO Trade Name, Opti-free Express, Clear Care, and UltraCare) and tested for survival. Plates were examined over the following week for growth. Results: Strain type and solution affected survival. MPSs were ineffective, with 100% survival of all strains at 6-hour exposure. Hydrogen peroxide systems were more effective, with survival of 3/5 strains (Clear Care) and 1/5 strains (UltraCare) at 6 hours. The Chicago-area tap water strain was most resistant. Among hydrogen peroxide systems, no statistically significant difference in Acanthamoeba survival existed with taurine inclusion. Conclusions: Recent clinical and tap water Acanthamoeba strains, representing proven human pathogens and/or household strains, were highly virulent against contact lens solutions. The Chicago-area tap water strain was most resilient, a concern if tap water is contributing to the AK increase. Results further differentiated resistance among T4 strains, highlighting the importance of multiple strain testing.