Novel fusion protein protects against adherence and toxicity of enterohemorrhagic Escherichia coli O157:H7 in mice

Infection with Escherichia coli (E. coli) O157:H7 may develop into bloody diarrhea, or hemorrhagic uremic syndrome (HUS), which usually causes kidney failure or even death. Considered as the pathogenesis mechanism of E. coli O157:H7 infection, attachment or adhesion that is directly mediated by intimin is the first step of E. coli O157:H7 interaction with its host, and all these serious sequelae are mainly due to Shiga toxins (Stxs) released by E. coli O157:H7. In this study, a novel SSI fusion protein that contains the critical toxin-antigens Stx2B and Stx1B, and the critical adhesion-antigen fragment Int281 was constructed. The protein induced complete immune protection, with both anti-toxin and anti-adhesion effects. The dominant increase in IgG1 and the high level of Th2-typical cytokine (IL-4 and IL-10) expression showed that SSI significantly induced Th2-mediated humoral immune response. In the mouse model, the SSI fusion protein not only elicited neutralizing antibodies against both Stx1 and Stx2 toxins, but also induced a high level of anti-adhesion antibodies. The SSI-immunized mice did not show any pathologic changes. SSI provides evident protection with two-time immunization against a highly lethal dose of E. coli O157:H7.