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1 From the Departments of Microbiology, Immunology, and Parasitology and 2 Pathology, Louisiana State University (LSU) Health Sciences Center, New Orleans, Louisiana; 5 Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland; and the 4 LSU Eye Center, New Orleans, Louisiana.
PURPOSE. To determine the pathogenic role of 
- and 
-toxin in a rabbit model of Staphylococcus aureus keratitis.
METHODS. S. aureus strains Newman (expressing -toxin), Newman 
hlg (deficient in -toxin), Newman hlg/pCU1 hlg+ (chromosomal -toxin–deficient mutant rescued by a plasmid encoding -toxin), and Newman hla (-toxin–deficient) were intrastromally injected into rabbit corneas. Eyes were scored by slit lamp examination (SLE), and bacterial colony-forming units (CFU) per cornea were determined at 15, 20, and 25 hours after infection. Histologic examination of corneas was performed. Rabbits were immunized against -toxin and subsequently challenged with S. aureus strain Newman. Western blot analyses of culture supernatants were performed to detect -toxin production.
RESULTS. All strains grew equivalently, producing approximately 7 log CFU per cornea at 25 hours after infection. SLE scores at 20 and 25 hours after infection revealed that strains Newman hlg and Newman hla, although virulent, caused significantly less ocular damage and inflammation than their parent or the -toxin genetically rescued strain (P 
0.0006). Histologic and SLEs revealed that all strains except Newman hla produced corneal erosions. Rabbits immunized actively or passively to -toxin had reduced SLE scores (P 0.0003 and P 0.0033, respectively) and no epithelial erosions when infected with strain Newman. Western blot analysis demonstrated that strains Newman and Newman hlg, but not Newman hla, produced -toxin.
CONCLUSIONS. These results illustrate that the virulence of strain Newman involves both - and -toxin, with -toxin mediating corneal epithelial erosions. An additional uncharacterized toxin could also be active in damaging the cornea.
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