Bacterial infections of the eye can have vision-threatening complications and often are associated with prosthetic devices such as contact lenses, scleral buckles, and intraocular lenses. Pseudomonas aeruginosa (PA) is one of the most common causes of bacterial keratitis. The central hypothesis of this proposal is that biofilm formation plays an important role in the pathogenesis of ocular infections of PA and that an understanding of the biology and genetics of Pseudomonas aeruginosa biofilm formation will have relevance to the development of novel antimicrobial therapies. Bacteria grow as planktonic (or free-living) cells or as surface-attached communities known as biofilms. Biofilm formation contributes to the pathogenesis of many clinical infections associated with prosthetic devices by allowing bacteria to persist on abiotic surfaces which come in contact with the body, by facilitating colonization of biotic surfaces and by rendering bacteria more resistant to antimicrobial agents. However, the relevance of biofilm formation to ocular infections has not been extensively studied. Bacterial keratitis caused by PA will be the model system studied in this project. Existing biofilm mutants of PA, as well as additional mutants that will be developed in the course of the project, will be used to elucidate the biology and genetics related to PA biofilm formation on abiotic and biotic surfaces relevant to the eye. The functions mutated in these strains may define novel drug targets. In addition, inhibitor studies may identify new classes of compounds that prevent and/or eliminate eye infections. The ability of growth in a biofilm to render PA resistant to the innate immune system, specifically the human B-defensin (hBD) 1 and 2 will be investigated. hBD 1 and 2 are recently described antimicrobial peptides secreted by the corneal and conjunctival epithelium. hBD 1 and 2 are active against PA under planktonic conditions, but have not been tested against organisms growing in a biofilm. If biofilm-based resistance exists, it would presumably contribute to keratitis and identification of genes that play a role in this process may be novel targets for rendering biofilm bacteria sensitive to antibiotics and defensins. If biofilm and planktonic cells are as equally sensitive to hBD-l and hBD-2, this would suggest that B-defensins can bypass biofilm-specific biocide resistance, and furthermore, these compounds (or derivatives) might make excellent therapeutics to prevent and/or treat biofilm-based infections.
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