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

Abstract

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.

Bacillus cereus cellulitis from contaminated heroin

“…The clinical appearance of patients with clostridial gas gangrene is attributed to the production of toxins; it is assumed, although less well investigated, that B. cereus also produces toxins that are responsible for clinical signs and symptoms [19]. Its toxin library is known to include the emetic and diarrhoeal toxins more often associated with food poisoning [20].…”

Requirement offlhAfor Swarming Differentiation, Flagellin Export, and Secretion of Virulence-Associated Proteins inBacillus thuringiensis

“…8). Zymograms of the mutant were similar to those of the wild type, since both strains were able to secrete thuringiolysin O (pI values of about 6.2, 6.5, and 6.8), which was identified through the inhibition of its activity by cholesterol (36), hemolysin II (6), and/or hemolysin III (5), which have similar isoelectric points (pI values of about 8.2), and hemolysin IV (pI 5.5) (7,42).…”

Contribution of Membrane-Damaging Toxins to Bacillus Endophthalmitis Pathogenesis

“…The intraocular toxicity of B. cereus PC-PLC and SPH has been analyzed. Purified PC-PLC was toxic to retinal buttons in vitro and to the retina in vivo, whereas purified SPH was minimally toxic in vitro (4). A third toxin, phosphotidylinositol-phospholipase C (PI-PLC), has been suggested to be a virulence factor for L. monocytogenes (38,43) and S. aureus (12,29) but has been shown to be minimally toxic to retinal buttons in vitro (4).…”