March 2012
Volume 53, Issue 14
ARVO Annual Meeting Abstract  |   March 2012
The Effect of Low Concentrations of Benzalkonium Chloride on Acanthamoebal survival
Author Affiliations & Notes
  • Elmer Y. Tu
    Ophthalmology, University of Illinois at Chicago, Glenview, Illinois
  • Megan E. Shoff
    CDRH/OSEL/DB, FDA, Silver Spring, Maryland
  • Charlotte E. Joslin
    Ophthalmology/Visual Sciences, University Illinois at Chicago, Chicago, Illinois
  • Footnotes
    Commercial Relationships  Elmer Y. Tu, None; Megan E. Shoff, None; Charlotte E. Joslin, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 6214. doi:
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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)

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Purpose: : To determine the activity of low, clinically relevant concentrations of benzalkonium chloride (BAK) against various strains of acanthamoeba in an established in vitro model.

Methods: : 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.

Results: : 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.

Conclusions: : 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.

Keywords: Acanthamoeba • keratitis • drug toxicity/drug effects 

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