UC Berkeley

Pseudomonas aeruginosa keratitis is a sight-threatening complication of contact lens wear. Ordinarily, the ocular surface is effective against microbial infiltration through a variety of mechanical, anatomical, and immunological defense mechanisms which protect the cornea. However, contact lens wear, ocular injury and/or surgery predispose individuals to bacterial keratitis. In the case of contact lens wear, the Gram-negative bacterium Pseudomonas aeruginosa is the most frequently isolated causative agent. As the number of antimicrobial compounds effective against P. aeruginosa decreases, due to of the acquisition and spread of antibiotic resistance, there is a growing need for novel therapeutic approaches corneal infection. The fact that P. aeruginosa can cross the corneal epithelium into the stroma to cause disease in contact lens wearers suggest a compromise in host defense. However, little is known of the mechanisms by which bacteria reach the stroma after adherence to corneal epithelial cells and how contact lenses increase the incidence of P. aeruginosa infection. Our broad theoretical model to explain the pathogenesis of contact lens related P. aeruginosa infection is that contact lens wear, because it provides a surface for biofilm formation, enables bacteria to persist at the ocular surface for long enough to adapt to defense factors that otherwise limit their ability to penetrate the corneal epithelium. Candidate corneal epithelial defense factors that might limit their ability to penetrate and which could also provide the driving force for bacterial adaptation include epithelial expressed antimicrobial peptides. Corneal epithelial cells are known to express a number of antimicrobial peptides capable of killing P. aeruginosa; including hBD 1-3 and cathelicidin LL-37, and it is known that exposure to antimicrobial peptides can induce differential gene expression in bacteria. In this dissertation, the hypothesis that was explored addressed only specific components of the broad theoretical model: That under normal circumstances, antimicrobial peptides expressed by the corneal epithelium limit P. aeruginosa translocation of the epithelium, but that prolonged exposure to corneal epithelia induces differential bacterial gene expression which enhances epithelial traversal.