Heterogeneity observed in the components of hemolysin BL, an enterotoxin produced by Bacillus cereus

Hemolysin BL (HBL), a diarrheal enterotoxin originally isolated from Bacill us cereus strain F837/76, is composed of three antigenically distinct prote ins designated B, L-1, and L-2. All three components are required for biolo gical activity. Here, we report antigenic and physical variations in HBL co mponents produced by other B. cereus isolates. Reactions of partial identit y were observed in double gel immunodiffusion assays using antibodies to hi ghly purified B, L-1, and L-2 components of F837/76 and culture supernatant s of strains F837/76 and S1C. Western blot analysis showed that F837/76 pro duced one 38-kDa B protein, one 38-kDa L-1, and one 43-kDa L-2 protein. In strain SIG, two B (38 and 42 kDa), two L-1 (38 and 41 kDa), and one L-2 (43 kDa) proteins were detected. Further Western blot analysis of 127 B. cereus isolates showed that 90 prod uced one or more of the three HBL components. Approximately half of these 9 0 isolates (43/90; 48%) produced protein profiles which differed from that of F837/76. A total of four B, two L-1, and three L-2 component profiles wi th proteins of different sizes were observed. Individual strains produced v arious combinations of single or multiple bands of each component. In addit ion, some strains produced only one or two of the three HBL components. The public health significance of these strains is unknown, as all three compo nents are required for biological activity. The data presented here demonst rates a high degree of heterogeneity in HBL and provide the basis for furth er studies to characterize the variations in HBL and to determine the role of the variant components in pathogenicity. (C) 1999 Elsevier Science BN. A ll rights reserved.