EXTRACELLULAR VIRULENCE FACTORS IN BACILLUS-CEREUS ENDOPHTHALMITIS - METHODS AND IMPLICATION OF INVOLVEMENT OF HEMOLYSIN BL

Bacillus cereus is a common cause of highly fulminant posttraumatic an d metastatic endophthalmitis, Exotoxins or enzymes likely contribute t o the severity of the infection, but specific virulence factors have n ot been identified, We developed two methods for the identification of B. cereus ocular virulence factors. In an in vitro assay that allows screening of multiple samples, retinal toxicity was estimated by measu ring the release of lactate dehydrogenase from retinal buttons treated with B. cereus toxins. The results from this assay were confirmed wit h a sterile endophthalmitis model in which the histopathologic effect of intravitreally injected toxins was assessed. We tested pure hemolys in BL (HBL), a tripartite dermonecrotic vascular permeability factor o f B. cereus, and crude exotoxin (CET) preparations, consisting of conc entrated, cell-free B. cereus culture supernatant. In the in vitro ass ay, both CET and HBL caused rapid release of lactate dehydrogenase and retinal disintegration, In vivo, the toxins caused endophthalmitis cl inically characteristic of B. cereus within 4 h. Histological changes included rapid retinal necrosis and detachment, choroidal edema, detac hment and disruption of the retinal pigment epithelium, and rapid infi ltration of polymorphonuclear leukocytes, Neutralization of HBL in CET preparations inhibited toxicity in vitro by 54%, and pure HBL was les s toxic than CET with equal HBL contents in both methods, The results suggest that B. cereus ocular virulence is multifactorial and that HBL contributes to virulence.