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C. C. McCormick, A. R. Caballero, C. L. Balzli, A. Tang, R. J. O'Callaghan; A New Model of Experimental Staphylococcus aureus Conjunctivitis in Rabbits. Invest. Ophthalmol. Vis. Sci. 2009;50(13):852.
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© ARVO (1962-2015); The Authors (2016-present)
To date, there is no animal model of Staphylococcus aureus conjunctivitis and this study was undertaken to develop a reproducible and quantitative rabbit conjunctivitis model.
Three strains of S. aureus (UMCR1, a conjunctival isolate; Newman, a well characterized strain producing little alpha-toxin; strain 70490, an ocular MRSA isolate) were tested for virulence by injection of 105 colony forming units (CFU) into the rabbit conjunctiva (n ≥ 4 per strain). The pathological changes were scored by slit lamp examination (SLE) at 4, 8, 12, and 20 hours postinfection (PI); SLE scores were the sum of the grades (0 to 4) for five parameters (injection, chemosis, corneal edema, iritis, and pinpoint conjunctival hemorrhages). At 1, 2, 4, 8, 12, and 20 hours PI, rabbits were sacrificed and conjunctival homogenates were quantitatively cultured to determine the log number of CFU (± SEM) per conjunctiva.
Rabbit eyes infected with UMCR1 had a SLE score that steadily increased from 3.00 ± 0.57 at 4 hours PI to 13.25 ± 0.80 at 20 hours PI, a time at which the experiment was ended due to the severe hemorrhaging of the conjunctiva. At 1 hour PI, conjunctivas infected with UMCR1 contained 5.19 ± 0.25 log CFU and by 8 hours PI the number of bacteria reached a maximum of > 7 logs CFU, a number that was maintained until 20 hours PI. In contrast, the SLE scores at 20 hours PI of eyes injected with either Newman (0.81 ± 0.16) or 70490 (2.94 ± 0.47) were significantly lower than that of strain UMCR1 (P ≤ 0.0031). The number of CFU obtained from conjunctivas at 20 hours PI from conjunctivas injected with strain Newman (3.91 ± 0.75 logs) or strain 70490 (6.01 ± 0.05 logs) were significantly lower than that of conjunctivas injected with strain UMCR1 (P = 0.0313 and P < 0.0001, respectively).
The injection of strain UMCR1 into the rabbit conjunctiva results in a reproducible and quantifiable model of experimental S. aureus conjunctivitis that is suitable for measuring the effectiveness of antimicrobial agents and studying mechanisms of pathogenesis.
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