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Principal Investigator: Dr. Eric Ledbetter
Mentor: Dr. Thomas Kern
Contact Information: E-mail: ecl32@cornell.edu - Phone: 607-253-3060
Sponsor: American College of Veterinary Opthalmologists
Title: Pathogenic Phenotype of Pseudomonas Aeruginosa Isolates from Canine and Equine Ulcerative Keratitis and Normal Extraocular Flora
Annual Direct Cost: $5,000
Project Period: 11/01/04-11/30/05
The purpose of this study is to explore the relationship between Pseudomonas aeruginosa pathogenic phenotype and corneal disease in dogs and horses. Pseudomonas aeruginosa has traditionally been considered an extracellular pathogen; however, recent studies have determined that some strains are capable of invading and surviving within corneal epithelial cells. Pseudomonas aeruginosa isolates can now be divided into two distinct functional groups based upon their pathogenic behavior toward host cells. The cytotoxic group acts extracellularly and produces toxins that are directly damaging to corneal epithelial cells. The invasive group is capable of entering, residing, and multiplying within corneal epithelial cells. This intracellular location may protect invasive strains of Pseudomonas aeruginosa from the host immune response and certain antibiotics, most notably the aminoglycosides which are non-cell permeable.
Pseudomonas aeruginosa isolates from patients with ulcerative keratitis and patients without extraocular disease will be submitted for pathogenicity phenotyping to determine if strains are invasive or cytotoxic, based upon their ability to invade or kill corneal epithelial cells. Detailed signalment, historical, and clinical data will be collected from each ulcerative keratitis patient, including serial slit lamp biomicroscopic examinations and digital photography. Extensive in vitro antimicrobial susceptibility determinations will be performed on each isolate. Corneal tissues from patients with ulcerative keratitis infected with invasive Pseudomonas aeruginosa isolates will be submitted for transmission electron microscopy to document in vivo invasion of corneal epithelial cells.
Specific objectives of this study include: determination of the frequency of each pathogenic phenotype's involvement in ulcerative keratitis and its presence in the normal extraocular flora; assessment of differences in clinical appearance of corneal infection caused by cytotoxic and invasive strains; documentation of corneal epithelial invasion in vivo by the invasive phenotype; correlation of differences in signalment or historical data with a specific phenotype; and comparison of the in vitro antimicrobial susceptibility patterns of the cytotoxic and invasive strains in ulcerative keratitis with those of the normal extraocular flora.
The frequency of this bacterium's involvement in ulcerative keratitis in veterinary patients and the great severity of the resultant disease dearly attest to the importance of determining which pathogenic phenotypes are responsible for corneal disease in the dog and horse. To date, no studies have been published that examine the relative distribution of Pseudomonas aeruginosa pathogenic phenotypes involved in veterinary disease processes. This is likely the result of the relative novelty of this information and the extremely limited availability of the pathogenicity phenotyping assay.
Although routine pathogenicity phenotyping of Pseudomonas aeruginosa isolates is currently impractical in the clinical setting, knowledge of the frequency of each phenotype's involvement in canine and equine corneal disease will enhance our understanding of Pseudomonas aeruginosa pathogenic mechanisms and could improve therapies and outcomes for our patients. Empirical antimicrobial selection could be made more appropriately and interpretation of antimicrobial susceptibility determinations could be improved, as these assays do not consider the cell-permeability of the drugs in question.
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