Here, neutralization is achieved in the storage case during disinfection by using a platinum-coated disk or soluble catalase tablet which catalyzes the decomposition of hydrogen peroxide to water and oxygen. One-step hydrogen peroxide systems are available which do not require a separate neutralization step. However, hydrogen peroxide is toxic to the cornea and must be neutralized before lens wear to avoid pronounced stinging, lacrimation, hyperemia, and possible corneal damage ( 7, 8). It is active against the resistant cyst form of Acanthamoeba when used at a concentration of 3% with an exposure time of at least 4 to 6 h ( 5, 14). Hydrogen peroxide is an effective microbial disinfectant, destroying pathogens by oxidation ( 11). The two most common methods of contact lens disinfection are the multipurpose solutions in which a single solution is used for disinfecting, cleaning, and storing lenses and hydrogen peroxide-based systems. Therefore, compliance with recommended hygiene procedures for cleaning and disinfecting lenses is fundamental to safe contact lens use and hence the prevention of infection. Infection results from contamination of lens care products, notably the lens storage case, from which the organism adheres to the contact lens and is inoculated onto the cornea ( 6, 14).Īcanthamoeba keratitis is one of the most difficult ocular infections to treat ( 4). Contact lens wearers are most at risk from infection, accounting for approximately 95% of reported cases ( 22, 23). Acanthamoeba cysts are resistant to desiccation ( 16), extremes of temperature from −20 to 56☌ ( 1, 12), and most disinfectants at working concentrations ( 13).Īcanthamoeba is an opportunistic pathogen, causing fatal encephalitis in the immunocompromised host ( 19) and, more frequently, a potentially blinding infection of the cornea termed acanthamoeba keratitis ( 4, 14). The organism is characterized by a life cycle of a feeding and dividing trophozoite, which in response to adverse conditions can form a dormant cyst stage ( 21). The cysticidal activity of one-step systems could be improved if neutralization rates were retarded.Īcanthamoeba is a genus of free-living amoeba found in most soil and water habitats ( 21).
One-step systems are less effective against Acanthamoeba cysts due to rapid peroxide neutralization. Variation in cyst killing occurs between peroxide solutions, possibly due to formulation differences. Two-step systems are cysticidal providing contact times of at least 4 h are employed. No cysticidal activity was found with the peroxigen sodium perborate or the contact lens protein remover subtilisin A. Variation in the cysticidal rate was observed with two solutions that gave a 1.8- to 2.1-log kill at 4 h compared with 3.0 to 4.0 for the rest ( P < 0.05). All system peroxide solutions were cysticidal, giving a ≥3-log kill by 4 to 6 h. Both two-step systems were cysticidal, giving a ≥3-log kill at 4 h. Of the four one-step systems, only one showed some cysticidal activity, giving a 1.28 ± 0.41-log reduction. All disinfection systems were active against trophozoites, giving a ≥3-log (99.9%) kill within 1 h. Here, the activities of commercial peroxide systems and individual solutions against trophozoites and cysts of Acanthamoeba polyphaga were compared. Neutralization is achieved by adding a catalyst during the disinfection process (one-step) or afterwards (two-step). Lenses must be neutralized before use to avoid pronounced stinging and possible corneal damage. Hydrogen peroxide is used for contact lens disinfection due to its broad antimicrobial activity. Contact lens wearers are most at risk and account for some 95% of cases.
Acanthamoeba is a free-living amoeba causing a potentially blinding infection of the cornea.
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