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Infection and Immunity, September 2000, p. 5269-5276, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Evidence for Contribution of Tripartite Hemolysin BL, Phosphatidylcholine-Preferring Phospholipase C, and Collagenase to Virulence of Bacillus cereus Endophthalmitis

Douglas J. Beecher,1,* Timothy W. Olsen,2 Eileen B. Somers,1 and Amy C. L. Wong1

Food Research Institute, Department of Food Microbiology and Toxicology, University of Wisconsin---Madison, Madison, Wisconsin 53706,1 and Department of Ophthalmology, University of Minnesota, Minneapolis, Minnesota 554552

Received 13 March 2000/Returned for modification 17 May 2000/Accepted 17 June 2000

Bacillus cereus causes a highly fulminant endophthalmitis which usually results in blindness. We previously concluded that hemolysin BL (HBL), a tripartite necrotizing pore-forming toxin, is a probable endophthalmitis virulence factor because it is highly toxic to retinal tissue in vitro and in vivo. We also determined that B. cereus produces additional retinal toxins that might contribute to virulence. Here we fractionated crude B. cereus culture supernatant by anion-exchange chromatography and found that in vitro retinal toxicity was also associated with phosphatidylcholine-preferring phospholipase C (PC-PLC). The pure enzyme also caused retinal necrosis in vivo. We showed that phosphatidylinositol-specific PLC and sphingomyelinase were nontoxic and that two hemolysins, cereolysin O and a novel hemolysin designated hemolysin IV, were marginally toxic in vitro. The histopathology of experimental septic endophthalmitis in rabbits mimicked the pathology produced by pure HBL, and both HBL and PC-PLC were detected at toxic concentrations in infected vitreous fluid. Bacterial cells were first seen associated with the posterior margin of the lens and eventually were located throughout the lens cortex. Detection of collagenase in the vitreous humor suggested that infiltration was facilitated by the breakdown of the protective collagen lens capsule by that enzyme. This work supports our conclusion that HBL contributes to B. cereus virulence and implicates PC-PLC and collagenase as additional virulence factors.

* Corresponding author. Present address: Hazardous Materials Response Unit, Building 12, FBI Academy, Quantico, VA 22135. Phone: (703) 632-4679. Fax: (703) 632-5430. E-mail: dbeecher{at}fbiacademy.edu.

Infection and Immunity, September 2000, p. 5269-5276, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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