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(Investigative Ophthalmology and Visual Science. 2007;48:5125-5131.)
© 2007 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.07-0320
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Age-Related Differences in Rabbits during Experimental Staphylococcus aureus Keratitis

Richard J. O’Callaghan,1,2 Clare C. McCormick,1,2 Armando R. Caballero,1,2 Mary E. Marquart,1,2 Hattie P. Gatlin,3 and Jonathan D. Fratkin3

1From the Departments of Microbiology and 3Pathology, University of Mississippi Medical Center, Jackson, Mississippi; and the 2Department of Microbiology, Immunology and Parasitology, Louisiana State University Health Sciences Center, New Orleans, Louisiana.

PURPOSE. To analyze age-related changes in susceptibility to experimental Staphylococcus aureus keratitis and purified {alpha}-toxin in rabbits.

METHODS. Intrastromal injection of S. aureus (100 colony-forming units [CFUs]) induced keratitis in young (6–8 weeks) and aged (approximately 30 months) New Zealand White rabbits. Bacteria and polymorphonuclear leukocytes (PMNs) per cornea were quantified. Purified {alpha}-toxin at 1, 10, 25, or 50 hemolytic units (HU) or heat-inactivated {alpha}-toxin was intrastromally injected into corneas, and pathologic changes were determined by slit lamp examination (SLE) and histopathologic analysis. {alpha}-Toxin hemolysis assays were performed using erythrocytes from young and aged rabbits.

RESULTS. S. aureus keratitis produced significantly higher SLE scores in young rabbits than in aged rabbits at 15, 20, and 25 hours postinfection (PI; P ≤ 0.001); aged rabbits essentially recovered from S. aureus keratitis by 7 days PI. At 25 hours PI, numbers of CFUs and PMNs in corneas of young and aged rabbits were equivalent (P ≥ 0.6); the bacterial burden in aged rabbits declined by 5 logs per cornea from day 1 to day 7 PI. Intrastromal injection of ≥10 HU {alpha}-toxin also produced significantly more disease in young than in aged rabbit corneas (P ≤ 0.05), whereas 1 HU or heat-inactivated toxin yielded negligible pathologic changes in either group. Hemolysis assays of erythrocytes from young rabbits demonstrated greater susceptibility to {alpha}-toxin compared with those from aged rabbits.

CONCLUSIONS. Corneas and erythrocytes of young rabbits, relative to aged rabbits, are significantly more susceptible to S. aureus keratitis and to {alpha}-toxin.






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Copyright © 2007 by the Association for Research in Vision and Ophthalmology