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A.R. Caballero, B.A. Thibodeaux, J.J. Reed, M.E. Marquart, C.C. McCormick, K.S. Monds, R.J. O'Callaghan; Virulence of Staphylococcus epidermidis Strains in the Rabbit Cornea . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2626.
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© ARVO (1962-2015); The Authors (2016-present)
To study the ocular virulence of Staphylococcus epidermidis strains in a rabbit model of keratitis.
S. epidermidis strains (29 ocular isolates, 1 ATCC strain) were analyzed for hemolysis in rabbit and sheep blood agar at 37ºC for 24 hours, and for extracellular protease activity in gelatin zymograms. Three strains were selected based on the presence or absence of hemolysis and gelatinase activity (ATCC 14990, S. epi 30108, S. epi 30111). Rabbit corneas (n = 6) were injected intrastromally with 100 colony forming units (CFU) of each individual strain per group. Slit lamp examination (SLE) scoring was performed at 20 and 25 hours post infection (PI), and the log number of CFU per cornea was determined at 25 hours PI. SLE scores were analyzed by nonparametric one–way analysis of variance (Krustal–Wallis test) and Wilcoxon’s test. CFU determinations were analyzed by Student’s t tests between least–squared means.
Hemolysis on rabbit and sheep blood agar was observed for 26 and 17 out of 30 strains, respectively. Twenty five out of 30 strains exhibited gelatinase activity, with 1 strain exhibiting proteolytic activity at ∼ 40 kDa, 12 strains at ∼ 60 kDa, 3 strains at 69 kDa, and 9 strains at both ∼ 40 and 60 kDa. SLE scores, hemolysis, and gelatinase activity of selected strains are shown in the table below.
SLE scores at both time points were significantly different between the strains. There was no significant difference in log CFU scores between the strains, (ATCC 14990, 6.89 ± 0.08; S. epi 30108, 6.57 ± 0.14; S. epi 30111, 6.86 ± 0.20).
There is a difference in corneal virulence among S. epidermidis strains. S. epidermidis strain 14990 was essentially avirulent in the rabbit eye. S. epidermidis strain 30108, which was hemolytic, exhibited moderate virulence at 25 hours PI. S. epidermidis strain 30111, which secreted significant gelatinase activity, exhibited the greatest virulence at 20 and 25 hours PI. Secretion of extracellular proteases could contribute to the observed corneal virulence.
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