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DC Cochran, ST Kane, M Gominet, D Lereclus, MC Callegan; Contribution of Membrane-damaging Toxins to Bacillus Endophthalmitis Pathogenesis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1601.
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Purpose: To analyze the contribution of membrane-damaging toxins (phosphatidylinositol-specific phospholipase C [PI-PLC], phosphatidylcholine-specific phospholipase C [PC-PLC] and sphingomyelinase [SPH] to the pathogenesis of experimental Bacillus endophthalmitis. Methods: Isogenic mutants were constructed by insertional mutagenesis with lacZ into B. thuringiensis genes encoding PI-PLC (Δ;plcA), PC-PLC (Δ;plcB), or SPH (Δ;sphA). Rabbit eyes were injected intravitreally with 2 log10 CFU BT407 (wild type), Δ;plcA, Δ;plcB, or Δ;sphA. Pathogenicity was compared throughout the course of infection by biomicroscopy, histology, ERG, and bacterial and inflammatory cell quantitation. Results: No SPH activity was detected in filtered supernatants of all strains. Wild type and toxin-deficient mutants grew at comparable rates in vitro and in rabbit eyes. The rate of decrease in retinal responses of eyes infected with the toxin-deficient mutants were similar to that of wild type, with all strains resulting in elimination of retinal function by 18 h. Wild type BT407 and Δ;sphA each caused significant increases in implicit times of ERG b-wave responses at 6 h, but Δ;plcA and Δ;plcB did not. All strains elicited significant inflammatory cell influx into the anterior chamber by 12 h. Histologically, eyes infected with each strain were indistinguishable throughout the infection course. Conclusion:In this model, deficiencies in PI-PLC and PC-PLC had no effect of the course or severity of experimental Bacillus endophthalmitis. The role of SPH in endophthalmitis remains in question. ERG b-wave alterations early in infection may mark the mark the beginnings of specific neuronal or glial cell dysfunction. Whether these findings extend to the pathogenesis of B. cereus endophthalmitis is presently under investigation.
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