Role of hemolysin BL in the pathogenesis of extraintestinal Bacillus cereus infection assessed in an endophthalmitis model

Bacillus cereus is a rare cause of serious human infection but, paradoxical ly, causes one of the most severe posttraumatic or endogenous infections of the eye, endophthalmitis, which frequently results in blindness. The virul ence of B. cereus endophthalmitis historically has been attributed to toxin production. We therefore sought to examine the contribution of the dermone crotic toxin, hemolysin BL, to the pathogenesis of B. cereus infection in a n endophthalmitis system that is highly amenable to study. The pathogenesis of infection resulting from intravitreal injection of 10(2) CFU of either a clinical ocular isolate of B. cereus producing hemolysin BL (HBL+) or an isogenic mutant in this trait (HBL-) was assessed bacteriologically and by slit lamp biomicroscopy, electroretinography, histology, and inflammatory c ell enumeration. Both HBL+ and HBL- strains evoked severe intraocular infla mmatory responses as early as 12 h postinfection, with complete loss of ret inal responsiveness by 12 h. The infections caused by both strains spread o f the infection to adjacent tissues by 18 h. No significant differences in intraocular bacterial growth (P greater than or equal to 0.21) or inflammat ory changes (P greater than or equal to 0.21) were observed in eyes infecte d with either HBL+ or HBL- strains during the course of infection. The leve l of retinal responsiveness was greater in HBL- infected eyes than in HBL+- infected eyes at 6 h only (P = 0.01). These results indicate that hemolysin BL makes no essential contribution to the severe and rapid course of infec tion in the endophthalmitis model.