Some potential pathogenic traits of gram-negative bacteria isolated during ocular inflammation and infections

Background : Bacterial colonisation of contact lenses is believed to be important in the production of microbial keratitis and acute inflammatory reactions. The aim of the current study was to examine strains isolated from ocular infections and non-infectious ocular inflammatory conditions for their ability to adhere to contact lenses and epithelial cells and to stimulate the release of chemotactic substances from epithelial cells. Methods : Bacterial adhesion to contact lenses and bovine corneal or conjunctival cells was studied by adhesion assay. Agglutination of human red blood cells by bacteria was demonstrated by haemagglutination. The chemoattractants released from corneal epithelial cells exposed to bacteria was assessed by polymorphonuclear leukocytes (PMN) chemotaxis. Results : Strains of P. aeruginosa adhered better on the contact lenses than strains of other gram-negative bacteria (p = 0.004). H. influenzae strains isolated from conjunctivitis produced haemagglutination. Leukotriene B₄ was released from corneal epithelial cells after stimulation by the gram-negative bacteria. Conclusion : This study has identified several potential pathogenetic traits of gram-negative bacteria that may contribute to ocular infection and/or inflammation. It has been estimated that 70 per cent of microbial keratitis cases associated with contact lens wear involve P. aeruginosa and this study has shown that this bacterial species adheres in large numbers to contact lenses. This increased adhesion to contact lenses may be one of the reasons for the preponderance of this species in these infections. The finding that strains could stimulate corneal epithelial cells to release chemotactic factors that specifically recruit PMN indicates a mechanism for producing corneal infiltration.