A Noncytolytic alpha Toxin Recombinant Protein Protects Turkeys Against Clostridium septicum Challenge

Clostridium septicum and its associated cytolytic alpha toxin, along with several other clostridial species, has been implicated as the causative agent of gangrenous dermatitis. A recombinant noncytolytic C. septicum alpha toxin (NCAT) peptide was developed for use as a vaccine and demonstrated to be safe at concentrations as high as 1 mg/ml. NCAT, used as a purified antigen, partially purified antigen, or in combination with native antigens, was compared to salt-fractionated a toxin combined with denatured C. septicum bacteria (native) in a vaccination trial. Three-day-old poults were placed into one of five groups and received two, 0.2-ml vaccinations 5 wk apart. Subcutaneous challenge with 3.2 X 10(7) log phase C. septicum resulted in 78% to 95% of the vaccinated birds surviving challenge compared to 48% of sham-injected controls. By ELISA analysis on NCAT-coated plates, birds receiving vaccines containing the recombinant NCAT peptide showed significantly higher blood serum antibody concentrations than did birds receiving vaccines containing native antigens or alum controls. Additionally, high levels of maternally transferred antibodies reactive to NCAT-purified antigens found in the pre-immune sera from naive 3-day-old poults suggest that the tertiary structure of the NCAT peptide has a high homology to the native protein structure. In conclusion, our study showed that the use of a vaccine comprised of a noncytolytic recombinant alpha toxin peptide antigen provided clinical protection equal to the use of vaccines formulated with inactivated native proteins at a reduced overall cost.