Evidence for Complex Formation of the Bacillus cereus Haemolysin BL Components in Solution

Haemolysin BL is an important virulence factor regarding the diarrheal type of food poisoning caused by . However, the pathogenic importance of this three-component enterotoxin is difficult to access, as nearly all natural culture supernatants additionally contain the highly cytotoxic Nhe, the second three-component toxin involved in the aetiology of -induced food-borne diseases. To better address the toxic properties of the Hbl complex, a system for overexpression and purification of functional, cytotoxic, recombinant (r)Hbl components L₂, L₁ and B from was established and an deletion mutant was constructed from reference strain F837/76. Furthermore, 35 hybridoma cell lines producing monoclonal antibodies (mAbs) against Hbl L₂, L₁ and B were generated. While mAbs 1H9 and 1D8 neutralized Hbl toxicity and thus, represent important tools for future investigations of the mode-of-action of Hbl on the target cell surface, mAb 1D7, in contrast, even enhanced Hbl toxicity by supporting the binding of Hbl B to the cell surface. By using the specific mAbs in Dot blots, indirect and hybrid sandwich enzyme immuno assays (EIAs), complex formation between Hbl L₁ and B, as well as L₁ and L₂ in solution could be shown for the first time. Surface plasmon resonance experiments with the rHbl components confirmed these results with K values of 4.7 × 10 M and 1.5 × 10 M, respectively. These findings together with the newly created tools lay the foundation for the detailed elucidation of the molecular mode-of-action of the highly complex three-component Hbl toxin.