(from abstract). Bacterial keratitis can result in blindness or a loss of visual acuity through a pathologic process that involves the interaction of bacteria, their products, and the host reaction to bacterial proteins. The infections are caused with almost equal frequency by Gram-positive (e.g., Staphylococcus or pneumococcus) or Grain- negative (e.g., Pseudomonas or Serratia) bacteria. While the outcomes of these bacterial infections are similar, research conducted in this laboratory has shown that the fundamental mechanisms differ dramatically. For Gram-positive bacteria, a hemolytic exotoxin is the prime mediator of tissue damage. In Pseudomonas or Serratia keratitis, bacterial proteases are essential for the intra-corneal stage of infection. The long-term goal of this research is to determine the molecular events mediating keratitis and to devise means to interrupt those reactions that result in irreversible tissue damage. The objectives of the present proposal are to determine the molecular properties of Pseudomonas protease IV, an extracellular enzyme associated with corneal virulence. This protease is produced by nearly all Pseudomonas ocular isolates and a mutant deficient in this enzyme is attenuated in animal models of keratitis. The PI's laboratory has very recently determined the DNA sequence of the gene for protease IV making possible for the first time detailed molecular biology studies.
The specific aims are: 1) construct a plasmid that codes for functional protease IV and determine if the plasmid can augment the virulence of its host bacterium 2) identify the amino acids that comprise the active site of this enzyme providing the data will guide the development of a protease inhibitor, 3) prepare allele replacement mutants deficient in the protease IV gene and perform genetic rescue experiments to prove the relationship between protease IV and corneal damage, and 4) test synthetic peptides for use an immunogens in developing an immune state protective against the tissue damage associated with Pseudomonas keratitis. The results of these studies are anticipated to provide new knowledge upon which can be based chemotherapeutic or immunologic means to limit the severity of Pseudomonas corneal infections.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Study Section
Visual Sciences A Study Section (VISA)
Program Officer
Fisher, Richard S
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Louisiana State University Hsc New Orleans
Schools of Medicine
New Orleans
United States
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Tang, Aihua; Caballero, Armando R; Marquart, Mary E et al. (2013) Pseudomonas aeruginosa small protease (PASP), a keratitis virulence factor. Invest Ophthalmol Vis Sci 54:2821-8
Tang, Aihua; Marquart, Mary E; Fratkin, Jonathan D et al. (2009) Properties of PASP: a Pseudomonas protease capable of mediating corneal erosions. Invest Ophthalmol Vis Sci 50:3794-801
McCormick, C C; Hobden, J A; Balzli, C L et al. (2007) Surfactant protein D in Pseudomonas aeruginosa keratitis. Ocul Immunol Inflamm 15:371-9
Thibodeaux, Brett A; Caballero, Armando R; Marquart, Mary E et al. (2007) Corneal virulence of Pseudomonas aeruginosa elastase B and alkaline protease produced by Pseudomonas putida. Curr Eye Res 32:373-86
Malloy, Jaret L; Veldhuizen, Ruud A W; Thibodeaux, Brett A et al. (2005) Pseudomonas aeruginosa protease IV degrades surfactant proteins and inhibits surfactant host defense and biophysical functions. Am J Physiol Lung Cell Mol Physiol 288:L409-18
Thibodeaux, Brett A; Caballero, Armando R; Dajcs, Joseph J et al. (2005) Pseudomonas aeruginosa protease IV: a corneal virulence factor of low immunogenicity. Ocul Immunol Inflamm 13:169-82
Marquart, Mary E; Caballero, Armando R; Chomnawang, Mullika et al. (2005) Identification of a novel secreted protease from Pseudomonas aeruginosa that causes corneal erosions. Invest Ophthalmol Vis Sci 46:3761-8
Marquart, Mary E; Dajcs, Joseph J; Caballero, Armando R et al. (2005) Calcium and magnesium enhance the production of Pseudomonas aeruginosa protease IV, a corneal virulence factor. Med Microbiol Immunol 194:39-45
Caballero, Armando; Thibodeaux, Brett; Marquart, Mary et al. (2004) Pseudomonas keratitis: protease IV gene conservation, distribution, and production relative to virulence and other Pseudomonas proteases. Invest Ophthalmol Vis Sci 45:522-30
Thibodeaux, Brett A; Dajcs, Joseph J; Caballero, Armando R et al. (2004) Quantitative comparison of fluoroquinolone therapies of experimental gram-negative bacterial keratitis. Curr Eye Res 28:337-42

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