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Elmer Y. Tu, Megan E. Shoff, Charlotte E. Joslin; The Effect of Low Concentrations of Benzalkonium Chloride on Acanthamoebal survival. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6214.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the activity of low, clinically relevant concentrations of benzalkonium chloride (BAK) against various strains of acanthamoeba in an established in vitro model.
Trophozoites of a single strain each of Acanthamoeba castellanii, Acanthamoeba hatchetti, and Acanthamoeba polyphaga were incubated in non-nutrient amoeba saline + Enterobacter aerogenes. Three replicate exposures to three solutions of BAK to achieve final concentrations of 0.001%. 0.002% and 0.003% with unsupplemented amoeba saline acting as a control were performed. Samples were taken at 30 minutes, and 1.5, 2.5, 4, 5.5, and 7 hours after exposure and immediately quantified. Amoeba counts were estimated using the most probable number method (MPN), as previously described, utilizing serial dilutions.
Of the three reference strains tested, A. castellanii was the most resistant species tested demonstrating less than 1 log unit of reduction at any time point with BAK 0.001%, but achieving an average 2 log unit reduction at 120 minutes exposure with BAK 0.003%. All three concentrations of BAK were able to achieve 2 log unit reductions at 120 minutes for both A. hatchetti and A. polyphaga. With the exception of A.castellani, significant inhibition with BAK 0.003% was observed in at the earliest time point tested, 30 minutes, with a range of 2.5 to 4 log unit reductions. All strains demonstrated an inhibitory effect in both a concentration-dependent and time-dependent fashion.
Small concentrations of BAK, below that seen in most commercial eyedrop formulations can result in a significant and profound reduction in the number of acanthamoebal organisms which is not only strain-dependent, but also time- and concentration-dependent. The in vitro behavior of all types of ophthalmic preservatives should be accounted for in both pre-market testing for its potential to confound results, but also in their potential anti-microbial effects when applied to the ocular surface in regards to clinical outcome and culture yield.
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