Interactions between the constitutive host defences of tears and Staphylococcus epidermidis

As part of the normal microbiota of the external eye, Staphylococcus epidermidis has probably developed strategies to overcome tear defences. The interaction of this bacteria with constitutive tear proteins was examined. Isolates of S. epidermidis grown in 10% serum or artificial tear fluid containing lysozyme or lactoferrin were resistant to the action of these proteins. Using ELISA, cell wall binding of C3, vitronectin and lactoferrin differed quantitatively between strains and in closed-eye compared to open-eye conditions. No differences were observed between ocular and non-ocular strains. This suggests that ocular isolates originate from the general host microbiota and S. epidermidis isolates are resistant to individual constitutive tear proteins.