B-cell epitope KT-12 of enterohemorrhagic Escherichia coli O157:H7: a novel peptide vaccine candidate.

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is associated with hemorrhagic colitis, thrombotic thrombocytopenic purpura, and hemolytic-uremic syndrome in humans. B-cell epitopes of intimin γ from EHEC O157:H7 were predicted and synthesized for evaluating their immunogenicity and protective effect and for screening a novel synthetic peptide vaccine. In the present study, five B-cell epitopes of IntC300 were predicted by Hopp-Woods, Chou-Fasman, Karplus-Schulz, Emini, Jameson-Wolf and Kolaskar-Tongaonakar analysis. One of them, KT-12 (KASITEIKADKT) was coupled with keyhole limpet hemocyanin, and used to immunize BALB/c mice three times by subcutaneous and intranasal injection. Mouse serum titers of IgG and IgA were assessed by indirect ELISA. Oral inoculation of EHEC O157:H7 resulted in infection and death of the mice. It was found that B-cell epitopes are located within or near the peptide segments 658-669, 711-723, 824-833, 897-914, 919-931. Both subcutaneous and intranasal immunization induced higher concentrations of IgG antibodies, as detected by indirect ELISA, and nasal-mucosal immunization induced the production of high concentrations of IgA antibodies. After infection with a lethal dose of EHEC O157:H7, the survival rate of mice that had received subcutaneous immunization was not significantly different from that of the control group (P > 0.05). On the other hand, mice that received intranasal immunization showed a better survival rate than the group that received subcutaneous immunization (P < 0.05). The synthesized antigenic peptide KT-12 induced mice to produce higher concentrations of IgG and IgA after immunization, but only intranasal immunization of KT-12 succeeded in protecting most mice from infection with EHEC O157:H7. This study suggests that the synthesized antigenic peptide KT-12 is be a potential vaccine candidate against EHEC O157:H7.