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K.S. Monds, M.E. Marquart, J.M. Reed, A.R. Caballero, R.J. O'Callaghan; Alpha–Toxin Susceptibility Impacts Age–Related Differences in Experimental S. aureus Keratitis . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1883.
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© ARVO (1962-2015); The Authors (2016-present)
Define and analyze age–related changes in susceptibility to experimental keratitis
Intrastromal injections of 100 colony–forming units (CFU) of S. aureus strain 8325–4 were used to induce keratitis in young (8 – 10 weeks) and aged (approximately 36 months) New Zealand white rabbits (n = 6 corneas per group). Purified staphylococcal alpha–toxin (0.37 µg; 25.6 hemolytic units) was intrastromally injected into corneas of both young and aged rabbits (n = 6 corneas per group). Pathology was scored by two masked observers based on gross and slit–lamp examinations at 15, 20, and 25 hours post–infection, and at 1 and 3 hours following injection of toxin. Additionally, alpha–toxin–mediated hemolytic assays were performed using erythrocytes obtained from young and aged rabbits.
Slit–lamp examinations of pathology due to S. aureus keratitis produced scores significantly lower in aged than in young animals at 15, 20, and 25 hours post–infection (P ≤ 0.001). Log CFU’s were not significantly different between young and aged animals at the time of sacrifice (25 hours post–infection; P = 0.896). Intrastromal injection of purified alpha–toxin demonstrated significantly more pathology in young, as compared to aged, rabbit corneas (P ≤ 0.0005). Hemolysis assays revealed that erythrocytes of young rabbits were four–fold more susceptible to the action of staphylococcal alpha–toxin than those of their aged counterparts.
Corneas and erythrocytes of aged rabbits, relative to those of young rabbits, were significantly less susceptible to S. aureus keratitis and to alpha–toxin; this difference likely being mediated by decreased response to the action of alpha–toxin.
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