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Joseph J. Dajcs, Megan S. Austin, Gregory D. Sloop, Judy M. Moreau, Emma B. H. Hume, Hilary W. Thompson, Fionnuala M. McAleese, Timothy J. Foster, Richard J. O’Callaghan; Corneal Pathogenesis of Staphylococcus aureus Strain Newman. Invest. Ophthalmol. Vis. Sci. 2002;43(4):1109-1115.
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purpose. To determine the pathogenic role of γ- and α-toxin in a rabbit model of Staphylococcus aureus keratitis.
methods. S. aureus strains Newman (expressing γ-toxin), Newman Δhlg (deficient in γ-toxin), Newman Δhlg/pCU1 hlg + (chromosomal γ-toxin–deficient mutant rescued by a plasmid encoding γ-toxin), and Newman Δhla (α-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 α-toxin and subsequently challenged with S. aureus strain Newman. Western blot analyses of culture supernatants were performed to detect α-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 Δhlg and Newman Δhla, although virulent, caused significantly less ocular damage and inflammation than their parent or the γ-toxin genetically rescued strain (P ≤ 0.0006). Histologic and SLEs revealed that all strains except Newman Δhla produced corneal erosions. Rabbits immunized actively or passively to α-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 Δhlg, but not Newman Δhla, produced α-toxin.
conclusions. These results illustrate that the virulence of strain Newman involves both α- and γ-toxin, with α-toxin mediating corneal epithelial erosions. An additional uncharacterized toxin could also be active in damaging the cornea.
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