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David J. McCanna, Lyndon W. Jones; Membrane Permeability Of Staphylococcus Aureus Aggregates Exposed To Contact Lens Care Solutions. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6089.
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Microbial keratitis and corneal infiltrates have been associated with the development of bacterial aggregates (biofilms) on the surface of contact lens cases. Contact lens case contamination with biofilms occurs often due to the resistance of the bacterial aggregates to the antimicrobials present in contact lens care solutions. This study investigated the ability of contact lens care solutions to damage the cell membranes of Staphylococcus aureus (SA) aggregates.
Staphylococcus aggregates were formed by growing the bacteria on Mueller-Hinton Agar, harvesting with physiological saline and washing using centrifugation (500 x g for 5 minutes). Commercial contact lens solutions evaluated contained the antimicrobials polyquaternium-1 (PQ1) and polyhexamethylene biguanide (PHMB), PHMB alone, PQ1 and alexidine (ALX), and PQ1 and ALDOX. Each solution was challenged with 5 x 10(7)cfu/ml of SA (ATCC 6538) for 4 hours. 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 for these two dyes, the number of cells with damaged cell membranes was determined.
The contact lens solution that caused the greatest damage to the SA cell membranes was the formulation based on PQ1-ALX, with 81% of all cells being permeable to PI. The other formulations caused some of the bacteria to lose membrane integrity (13 - 30%), but did not cause as much damage to the bacteria cell membranes (all p < 0.05) as the PQ1-ALX formulation.
One of the five lens care systems tested caused a substantial number of SA bacteria to lose membrane integrity. Although membrane damage is only one of the many mechanisms by which an antimicrobial can kill microorganisms, understanding the ability of contact lens care solutions to damage bacteria cell membranes in an aggregate formation could lead to improved formulations for eradicating biofilms from contact lens cases.
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