Selenium Contact Lens Hydrogel Polymer: Inhibition of both Gram Negative and Gram Positive Bacterial Biofilm Formation - A Study of Different Organo-Selenium Molecules

Abstract

 

Purpose

 

Biofilm formation on contact lenses has been cited as a possible cause of corneal infection and acute red eye. A contact lens that blocks biofilm formation should reduce the frequency of these clinically significant problems. Selenium compounds have the ability to catalyze the formation of superoxide radicals in the tear film, which are cytotoxic to bacteria. Previous studies had shown that it was harder to kill Gram-negative bacteria. Thus, this study investigated the effectiveness of different covalent organo-selenium molecules polymerized into a hydrogel.

 

Methods

 

Two different organo-selenium compounds were polymerized directly into a hydrogel. The inhibition of biofilm formation with the different organo-selenium hydrogels was investigated by incubating organo-selenium hydrogels and selenium free hydrogel in a nutrient broth containing Staphylococcus aureus or Pseudomonas aeruginosa for 24 hours at 37^oC. Biofilms were quantified by determining the CFU per lens. The plates were incubated at 37^oC for 24 hours and the CFU were counted. For confocal laser scanning microscopy (CLSM), we used the S. aureus strain AH1333 which constitutively expresses green fluorescent protein from plasmid pCM11 in the presence of 1 µg/ml erythromycin (Malone et al., 2009) and P. aeruginosa PAO1/pMRP9-1 which constitutively expresses green fluorescent protein from plasmid pMRP9-1 in the presence of 300 µg/ml carbenicillin. Dose response curves were also determined for the two different organo-selenium compounds.

 

Results

 

Colony forming unit assays showed total inhibition, representing over 7 logs of Staphylococcus aureus and Pseudomonas aeruginosa killing on organo-selenium polymerized hydrogels. Confocal laser scanning microscopy confirmed these results. However, it was found from the dose response studies that the selenium compound that was longer in length (distance of the selenium from the backbone of the polymer), could kill the gram-negative bacteria at a lower final concentration in the hydrogel.

 

Conclusions

 

The organo-selenium hydrogel polymers successfully blocked the formation of a bacterial biofilm on the polymer by Staphylococcus aureus and Pseudomonas aeruginosa in vitro. Organo-selenium molecules, which were different in structure, were successful in inhibiting biofilm formation at different concentration in the hydrogel.

 

 

Keywords: 477 contact lens • 594 microbial pathogenesis: experimental studies