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Angela Arana, Charles L. Balzli, Anastasia C. Weeks, Aihua Tang, Armando Caballero, Richard J. O'Callaghan; Pathogenesis of Staphylococcus aureus Endophthalmitis: Analysis of Alpha-Toxin and Gamma-Toxin in the Rabbit Anterior Chamber. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2772.
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Endophthalmitis caused by Staphylococcus aureus can involve extensive tissue damage through unknown mechanisms. Alpha-toxin and gamma-toxin are cytolytic toxins produced by S. aureus that can extensively damage the cornea. In these studies, the pathogenic effects of such toxins as well as the effectiveness of the inhibitors were analyzed in the rabbit anterior chamber.
The cytolytic activity of alpha-toxin or gamma-toxin, as well as their inhibition with chemical or antibody inhibitors, was measured by hemolysis assay. Purified gamma-toxin (25 hemolytic units), alpha-toxin (25 hemolytic units), or heat-inactivated toxin was injected into anterior chambers of rabbits to determine pathogenic effects. Also tested, was the susceptibility of the anterior chamber to four forms of concentrated culture supernatant of the highly virulent S. aureus UMCR1: 1) native, 2) heat-inactivated, 3) native with a cyclodextrin and cholesterol complex (CD-Chol), and 4) native supernatant with antibody to alpha-toxin. Pathologic changes of injected eyes were photographed and measured by slit-lamp examination (SLE) scoring and histopathology analysis.
Purified alpha- or gamma-toxin injected eyes had a SLE score of 7.9 and 6.5, respectively, at 5 hours post-injection and declined thereafter. Heat-inactivated toxin demonstrated no noticeable pathology. Concentrated UMCR1 supernatant caused extensive pathologic effects with a maximum SLE score of 8.8 by 20 hours post-injection. Histopathology demonstrated infiltration of neutrophils into the anterior chamber and surrounding tissues. Minor hemorrhaging and endothelial damage was observed along with edema of the iris. Treatment of supernatant-injected eyes with CD-chol significantly reduced the SLE scores to 6.5.
Tissues of the anterior chamber were found to be susceptible to alpha- or gamma-toxins and to the UMCR1 supernatant. The CD-chol inhibitor or antibody protected against the effects of alpha-toxin, but only CD-Chol was effective against the UMCR1 supernatant.
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