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In Vitro Evaluation of a Hypochlorous Acid Hygiene Solution on Established Biofilms

Romanowski, Eric G., M.S.; Stella, Nicholas A., B.S.; Yates, Kathleen A., B.S.; Brothers, Kimberly M., Ph.D.; Kowalski, Regis P., M.S.; Shanks, Robert M. Q., Ph.D.

doi: 10.1097/ICL.0000000000000456

Objectives: The purpose of this study was to determine whether a commercial formulation of hypochlorous acid hygiene solution (0.01%), Avenova, can destroy existing biofilms formed by ocular clinical bacterial isolates, including blepharitis isolates of Staphylococcus aureus and coagulase-negative staphylococci, and a keratitis isolate of Pseudomonas aeruginosa.

Methods: Biofilms grown in bacterial growth media on disposable contact lens cases were challenged with hypochlorous acid hygiene solution. At various time points, surviving bacteria were quantified by serial dilution and colony counts. Staphylococcus aureus biofilms formed on glass were challenged using a hypochlorous acid hygiene solution and imaged using vital staining and confocal laser scanning microscopy.

Results: Bactericidal activity (≥3 Log10; 99.9%) was observed for all tested bacterial species after a 30-min exposure. Staphylococcus aureus biofilms had a bactericidal level of killing by 10 min (P<0.01), Staphylococcus capitis by 5 min (P<0.001), Staphylococcus epidermidis by 30 min (P<0.001), and P. aeruginosa by 10 min (P<0.01). Confocal microscopy and crystal violet staining analysis of bacterial biofilms treated with hypochlorous acid solution both demonstrated that biofilm bacteria were readily killed, but biofilm structure was largely maintained.

Conclusions: Hypochlorous acid (0.01%) hygiene solution was able to achieve bactericidal levels of killing of bacteria in biofilms but did not disrupt biofilm structures. Susceptibility of tested staphylococcal blepharitis isolates varied by species, with S. capitis being the most susceptible and S. epidermidis being the least susceptible.

The Charles T. Campbell Ophthalmic Microbiology Laboratory (E.G.R., N.A.S., K.A.Y., K.M.B., R.P.K., and R.M.Q.S.), Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA; and Fox Center for Vision Restoration (R.M.Q.S.), Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA.

Address correspondence to Robert M. Q. Shanks, Ph.D., Eye and Ear Institute, 203 Lothrop Street, Pittsburgh, PA 15213; e-mail:

The authors have no funding or conflicts of interest to disclose.

Supported by NovaBay Pharmaceuticals, Inc., Research to Prevent Blindness, Inc., New York, NY; Eye and Ear Foundation of Pittsburgh, NIH Grants EY024785 and EY08098; Avenova Daily Lid and Lash Hygiene Solution was kindly donated by NovaBay, Pharmaceuticals, Inc.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial License 4.0 (CCBY-NC), where it is permissible to download, share, remix, transform, and buildup the work provided it is properly cited. The work cannot be used commercially without permission from the journal.

Accepted October 30, 2018

© 2018 Contact Lens Association of Ophthalmologists, Inc.