Quantitative diversity of 67 kDa protective antigen among serovar 2 strains of Erysipelothrix rhusiopathiae and its implication in protective immune response

Mouse monoclonal antibodies (MAbs), raised against the NaOH-extracted antig en of Erysipelothrix rhusiopathiae strain Kyoto (serovar 2), recognized two different epitopes on a single protein of molecular weight 67 kDa. The MAb s were classified as protective or non-protective against strain Fujisawa ( serovar 1). In immunoblotting analysis using the MAbs, fifteen wild strains were shown to contain different amounts of 67 kDa protective antigen. Each formalin-killed whole cell vaccine (bacterin) prepared from the fifteen wi ld strains conferred different levels of protection against strain Fujisawa in mice. Bacterins prepared from wild strains with larger amounts of 67 kD a protective antigen tended to give high levels of antigen-specific antibod y and better protection to mice. These results indicate that the amount of 67 kDa protective antigen which influences the induction of protective immu ne responses may vary substantially among the strains of E. rhusiopathiae ( serovar 2).