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R. C. Mercer, J. Cortez, P. Tran, T. Mosley, A. Hamood, T. W. Reid; Prevention of Staphylococcus aureus Biofilm Formation on Contact Lenses With Different Selenium Compounds. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1520.
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© ARVO (1962-2015); The Authors (2016-present)
To study the effectiveness of a Selenocystamine compound (which is a diselenide) versus a monoselenide selenium-salt compound at inhibiting Staphylococcus aureus biofilm formation on contact lenses.
First, coupling chemistry was done. Free carboxyl groups on the contacts were linked to the selenocytamine or the mono-selenide selenium salt solutions through a reduction reaction to create an amide bound. The control contact group was not subjected to this step. The testing and control group contacts were then placed in each well of a 24 well plate that contained 1ml of 1:25 tryptic soy broth and 300µM reduced glutathione inoculated with approximately 1500 microorganisms. The plates were incubated at 37°C for 16 hours. Contact lenses where then subjected to a 30 second washing in 1ml of phosphate buffered saline (PBS, pH 7.4) in a 24 well plate three times. One lens from the control and treatment group were sent to Scanning Electron Microscopy for further analysis. The remaining contacts from each group were resuspended in 2ml of PBS and vortexed vigorously with a small magnetic stirrer for one minute. Serial ten-fold dilutions were done on the suspension from each lens to 10-6. A lysogeny broth agar plate was spotted with 20µL of each dilution, and three plates were used per suspension solution. After letting the plates grow in a 37°C incubator for 16 hours, the number of colony forming units were determined and analyzed.
Chemiluminescent analysis of Se activity on contact lenses was done. Selenocystamine activity had 1554 CL units of activity and the Monoselenide Selenium salt had 9817 CL units of activity. Glutathione was used as the reducing agent.Data from the colony forming unit assay was analyzed by the Mann-Whitney Test (unpaired, nonparametric) with two-tail P value. The monoselenide selenium salt's P value was <0.0001 and selenocystamine's P value was 0.0002 when compared separately to the control lenses.SEM analysis verified the Selenium coated contact lenses had significantly decreased growth of S. aureus when compared to control groups.
This experiment demonstrates Selenium can be successfully attached to a solid substrate such as a contact lens and its ability to inhibit biofilm formation by a Gram-positive bacterium, S. aureus, remains. Analysis through chemiluminescence verified both selenium compounds were active. In the future, Selenium may be utilized as a coating on contact lenses to prevent their related infections caused by S. aureus.
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