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Infection and Immunity, July 1999, p. 3348-3356, Vol. 67, No. 7
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Pathogenesis of Gram-Positive Bacterial Endophthalmitis

Michelle C. Callegan,1,2 Mary C. Booth,1,2,3 Bradley D. Jett,1,2,dagger and Michael S. Gilmore1,2,3,*

Department of Ophthalmology,1 Department of Microbiology and Immunology,2 and Molecular Pathogenesis of Eye Infections Research Center, Dean A. McGee Eye Institute,3 University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma

Received 21 December 1998/Returned for modification 3 February 1999/Accepted 12 April 1999

The severity of endophthalmitis has been associated generally with the virulence of the offending pathogen. However, precisely what constitutes the virulence in intraocular infections remains ill defined. We therefore sought to identify the basis for virulence for three common ocular pathogens (Bacillus cereus, Enterococcus faecalis, and Staphylococcus aureus) in terms of intraocular growth rates, bacterial localization patterns, and the contribution of cell walls and secreted products to the pathogenesis of endophthalmitis. Rabbit eyes were injected intravitreally with (i) viable B. cereus, E. faecalis, or S. aureus, (ii) metabolically inactive B. cereus, E. faecalis, or S. aureus, (iii) sacculus preparations from each strain, or (iv) culture fluid containing products secreted by each strain. Eyes were assessed at various times following injection by slit lamp biomicroscopy, electroretinography (ERG), bacterial and inflammatory cell enumeration, and histology. B. cereus endophthalmitis followed a more rapid and virulent course than E. faecalis or S. aureus endophthalmitis, eliminating retinal responsiveness, as measured by ERG, by 12 h. Analysis of bacterial localization revealed that B. cereus uniquely migrated rapidly from posterior to anterior segment during infection. Although injection of neither metabolically inactive bacteria nor cell wall sacculi greatly affected ERG, significant intraocular inflammation was observed. Injection of B. cereus or S. aureus culture fluids caused both significant reductions in retinal responsiveness and significant intraocular inflammation, paralleling that seen in natural infections. The results demonstrate that toxins, intraocular localization, and, to a lesser extent, the intraocular host response to cell walls all contribute to the pathogenesis of B. cereus, S. aureus, and E. faecalis endophthalmitis in a pathogen-specific manner. The key pathophysiologic differences in these intraocular diseases highlight opportunities for optimizing conventional therapies and deriving new ones.

* Corresponding author. Mailing address: Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104. Phone: (405) 271-1084. Fax: (405) 271-8128. E-mail: mgilmore{at}aardvark.ou.edu.

dagger Present address: Department of Biology, Oklahoma Baptist University, Shawnee, Okla.

Infection and Immunity, July 1999, p. 3348-3356, Vol. 67, No. 7
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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