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Phillip Coburn, Frederick Miller, Michelle Callegan; The pathogenicity island-encoded AraC-type transcriptional regulator, PerA, contributes to the course and severity of Enterococcus faecalis endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):137.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the contribution of the AraC-type virulence gene regulator, PerA, in the development of Enterococcus faecalis endophthalmitis.
To evaluate the incidence of perA among endophthalmitis isolates, genomic DNA was prepared from 39 endophthalmitis isolates and PCR performed using perA-specific primers. To directly test whether PerA is involved in infection, we utilized a new mouse model of E. faecalis endophthalmitis to compare the course and severity of endophthalmitis caused by the clinical E. faecalis isolate E99 with that of an isogenic perA mutant, DBS01, and perA complemented strain GT101. 50 cfu of strains E99, DBS01, or GT101 were injected directly into the midvitreous of C57BL/6J mice. At 12 and 24 h postinfection, mice were subjected to electroretinography (ERG) and the percent ERG retention was calculated relative to the control, uninfected eye for each animal. Following ERGs, mice were euthanized and infected eyes harvested for quantitative determination of E. faecalis per eye.
PCR analysis of 39 isolates revealed that 23 were PCR positive for perA, suggesting an enrichment of this gene among endophthalmitis isolates, and consistent with our previous findings of enrichment among E. faecalis clinical isolates. During E. faecalis endophthalmitis, at 12 h postinfection, a statistically significant decrease in the %ERG retained for both A- and B-waves was observed in eyes infected with the perA mutant strain DBS01 compared to the wildtype E99 and perA complemented strain GT101. This suggested that inactivation of the perA gene might result in greater virulence in this model. At 24 h postinfection, there were no differences in %ERG retained between the strains. Quantitation of bacterial concentrations in infected eyes did not reveal a difference in growth rate, suggesting that PerA does not influence growth in the vitreous.
The results of this study demonstrate an enrichment of perA among endophthalmitis isolates, and suggest that PerA contributes to the course and severity of E. faecalis endophthalmitis. Further, our results suggest that PerA might serve as a direct or indirect repressor of virulence genes, and future studies will aim to identify and directly test these factors in the mouse endophthalmitis model.
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