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David McCanna, Jaclyn Chang, Lakshman Subbaraman, Lyndon Jones; Efficacy Of Contact Lens Solutions Against Achromobacter xylosoxidans Biofilms Using Confocal Microscopy. Invest. Ophthalmol. Vis. Sci. 2013;54(15):523.
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Biofilms of Achromobacter xylosoxidans (Ax) can develop in contact lens cases. These microorganisms can attach to the contact lens and cause microbial keratitis. This study evaluated the antimicrobial efficacy of contact lens solutions against Ax biofilms by measuring the damage to cell membranes of Ax using confocal microscopy.
Ax biofilms were formed by incubating the bacteria overnight on glass coverslips. The biofilms were then exposed to contact lens solutions for four hours. Commercial contact lens solutions evaluated contained the antimicrobials polyhexamethylene biguanide (PHMB), polyquaternium-1 (PQ1) and alexidine (ALX), and PQ1 and Aldox (AD). After exposure, the bacteria were stained with SYTO 9 and propidium iodide (PI). Using a confocal microscope with a 488nm laser and the appropriate emission filters the number of cells with damaged cell membranes was determined. In addition to evaluating contact lens solutions, four concentrations of benzalkonium chloride (BAK) 0.05%, 0.01%, 0.005% and 0.001% in phosphate buffer saline were also evaluated to demonstrate dose related effects at exposure times as short as 5 minutes.
The contact lens solution that caused the greatest damage to the Ax cell membranes was the formulation based on PQ1-ALX. The other formulations tested based on PHMB and PQ1 with AD caused some of the bacteria to lose membrane integrity but did not cause as much damage to the bacteria cell membranes (p < 0.05) as the PQ-ALX formulation. Dose effects of the preservative BAK could be seen at 5 minutes of exposure time. BAK at 0.005% and 0.01% caused an increase in the number of cells that were permeable to PI compared to the phosphate buffered control (48% and 62% respectively, p < 0.05). All of the Ax bacteria were permeable to PI after exposure to 0.05% BAK.
One of the five lens care systems tested caused a substantial number of Ax bacteria to lose membrane integrity. Also, this method was able to detect the effect different concentrations of BAK have on the membrane integrity of the Ax biofilm bacteria. Understanding the ability of antimicrobials to damage bacteria cell membranes could help in the development of lens care solutions that can reduce and/or eliminate Ax biofilms from lens cases.
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