Enhanced Killing of Acanthamoeba Cysts with a Plant Peroxidase-Hydrogen Peroxide-Halide Antimicrobial System

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Abstract
The activity of H 2 O 2 against the resistant cyst stage of the pathogenic free-living amoeba Acanthamoeba was enhanced by the addition of KI and either horseradish peroxidase or soybean peroxidase or, to a lesser degree, lactoperoxidase. This resulted in an increase in the cysticidal activity of 3% (wt/vol) H 2 O 2 , and there was >3-log killing in 2 h, compared with the 6 h required for comparable results with the peroxide solution alone ( P < 0.05). With 2% H 2 O 2 , enhancement was observed at all time points ( P < 0.05), and total killing of the cyst inoculum occurred at 4 h, compared with 6 h for the peroxide alone. The activity of sublethal 1% H 2 O 2 was enhanced to give 3-log killing after 8 h of exposure ( P < 0.05). No enhancement was obtained when KCl or catalase was used as a substitute in the reaction mixtures. The H 2 O 2 was not neutralized in the enhanced system during the experiments. However, in the presence of a platinum disk used to neutralize H 2 O 2 in contact lens care systems, the enhanced 2% H 2 O 2 system gave 2.8-log killing after 6 h or total cyst killing by 8 h, and total neutralization of the H 2 O 2 occurred by 4 h. In contrast, 2% H 2 O 2 alone resulted in 2 O 2 contact lens disinfection systems against Acanthamoeba cysts and prevention of acanthamoeba keratitis.