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C. L. Balzli, C. C. McCormick, A. R. Caballero, A. Tang, R. J. O'Callaghan; A Rabbit Model of Staphylococcus aureus Anterior Chamber Infection and the Effectiveness of Prophylactic Therapy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3109.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize a reproducible model of an active Staphylococcus aureus infection within the rabbit anterior chamber; a model for studying the pathogenesis of endophthalmitis and the effectiveness of prophylactic treatments.
The anterior chamber of rabbits was injected with 1 x 104 colony forming units (CFU) of S. aureus strain UMCR1. Eyes (n = 4 per time point) were photographed and pathological changes were scored by slit lamp examination (SLE) at 2, 4, 6, 8, 12, and 16 hours post-infection (PI). The aqueous humor of each eye (n ≥ 4 per time point) was quantitatively cultured to determine the CFU/ml. Pathology was also documented by histopathological analysis of the anterior chamber, and neutrophils in the aqueous humor were quantified using the myeloperoxidase assay. Gatifloxacin (300µg), lysostaphin (a bactericidal enzyme, 250µg), or tris-buffered saline was injected into the anterior chamber of rabbit eyes (n = 6 per group) and the treated eyes were infected 48 hours later with 104 CFU of UMCR1. At 6 hours PI, the aqueous humor was cultured to quantify the CFU/ml.
S. aureus strain UMCR1 grew steadily within the aqueous humor reaching 6.9 logs CFU/ml by 16 hours PI. SLE scores increased steadily due to conjunctival injection, edema, chemosis, severe iritis, and fibrin accumulation. Neutrophils accumulated in the aqueous humor increasing from 3.3 logs prior to infection to 5.6 logs by 16 hours PI. MICs for lysostaphin and gatifloxacin were 1.0 and 0.1 µg/ml, respectively. There were no bacteria recovered from eyes prophylactically treated with lysostaphin, which was a significant reduction (P < 0.001) from either gatifloxacin or tris-buffered saline injected eyes that yielded 3.1 and 3.4 logs CFU/ml of aqueous humor, respectively.
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