Protection against Shiga toxin 1 challenge by immunization of mice with purified mutant Shiga toxin 1

Shiga toxin 1 (Stx1) of enterohemorrhagic Escherichia coli O157:H7 was cloned, and four mutant Stx1s were constructed by site-directed mutagenesis with PCR. The wild-type and mutant Stx1s with amino acid replacements at positions 167 and 170 of the A subunit were purified by one-step affinity chromatography with commercially available Globotriose Fractogel, and the mutant Stxs were used for the immunization of mice. The mutant toxins were nontoxic to Vero cells in vitro and to mice in vivo and induced the immunoglobulin G antibody against the wild-type Stx1, which neutralized the cytotoxicity of Stx1. The induced antibody titers depended on the mutation at position 170 of the A subunit. The mice immunized with the mutant Stx1s were protected against a challenge of approximately 100 times the 50% lethal dose of the wild-type Stx1, suggesting that the mutant toxins are good candidates for toxoid vaccines for infection by Stx1-producing E. coli.