Binding of Staphylococcus aureus to fibronectin and glycolipids on corneal surfaces

Staphylococcus aureus is one of the most common pathogens of bacterial corneal ulcers. It is generally believed that the first step necessary in the development of an infection involves adherence of bacteria to host tissue. The mechanisms by which staphylococci adhere to ocular epithelium have not yet been defined. An in vitro assay was used to measure binding of S. aureus and Streptococcus pyogenes to a cornea epithelial cell line. Reduction of the amount of cell-surface fibronectin by proteinase treatment decreased the adherence of S. pyogenes to a greater degree than that of S. aureus. The significantly higher number of staphylococci adhering to the cells as compared with S. pyogenes (P < 0.001) suggests the presence of additional binding sites for S. aureus. Using a thin-layer chromatogram overlay assay, we showed binding of S. aureus to various glycolipids extracted from corneal epithelial cells and corneal tissue. S. aureus was found to bind to gangliosides and asialo-GM1, whereas S. pyogenes did not bind to any of these complex lipids. The increased adherence potential of S. aureus due to the ability to bind to glycolipids may provide a selective advantage for S. aureus and explain the prevalence of this organism in bacterial corneal ulcers.