Antimicrobial Properties Of Selenium Covalently Incorporated Into The Polymer Of Contact Lens Case Material

Abstract

Purpose: : Biofilm formation on contact lens cases is a serious problem since it allows bacteria to grow even in the presence of contact lens cleaning solution. Recently, silver as an antimicrobial was incorporated into contact lens cases, however, silver has several drawbacks. Any patient with silver or metal allergies cannot use these cases and silver has minimal effects against Staphylococcus aureus (S. aureus) and different fungi. In addition, silver is expensive and has to leach out of the case to be active. Thus, silver has a limited active half-life. In contrast, selenium does not have to leach out of the material to be active since it kills by the catalytic formation of superoxide radicals and it is much less expensive. Thus, this project was carried out to test the ability of selenium, covalently incorporated into the polymer of contact lens case material, to inhibit biofilm formation.

Methods: : Selenium monomers were made that allowed for the incorporation of selenium into the polymer of polypropylene. This material was then injection molded. The resulting material was tested for its ability to inhibit biofilm formation. S. aureus was tested since this bacteria was resistant to killing with silver. The S. aureus was allowed to grow in the presence of the polypropylene (with or without selenium) for 24 hours. The bacteria was then removed by vortexing and assayed. In one assay the bacterial concentration was determined by a colony forming unit assay (plating on agar). In another assay the bacteria was imaged by confocal laser scanning spectroscopy and then the biofilm was quantitated by COMSTAT analysis.

Results: : The selenium containing polypropylene showed 7.9 logs (complete) of inhibition against S. aureus and also was fully active after soaking in PBS for the equivalent of 8 weeks.

Conclusions: : The results showed that selenium covalently incorporated into a polypropylene polymer could total inhibit a S. aureus biofilm formation. This material could be injection molded and was still fully active after 2 months of soaking.

Keywords: contact lens • bacterial disease • Staphylococcus