Recombinant Lactococcus lactis-based oral vaccine expressing non-toxic alpha toxin domains of Clostridium septicum can offer protection against Clostridial dermatitis in turkeys

Clostridial dermatitis (CD), caused by the anaerobic spore-forming Clostridium septicum bacteria, is an important emerging disease of turkeys. Despite its economic burden on the poultry industry, there are no efficacious vaccines currently available for CD control in turkeys. We recently identified two non-toxic domains of C. septicum alpha toxin (ntATX), namely ntATX-D1 and ntATX-D2, and showed that subcutaneous immunization of turkeys with purified recombinant subunit ntATX proteins can offer protection against CD. In the present study, we used the pNZ8124-NICE vector®-based Lactococcus lactis (Str. NZ9000) cloning system to express ntATX-D1 and ntATX-D2 proteins, and immunized turkeys orally at 7, 8 and 9 weeks of age followed by a virulent C. septicum challenge at one-week post-last immunization. Results showed that while both ntATX-D1 and ntATX-D2 vectored-L. lactis vaccines could effectively prevent mortality, the ntATX-D2 carrying vaccine conferred significantly stronger protective immunity, as determined by the gross and histopathological evaluations. Additionally, the immunized birds were found to have antigen-specific serum IgY antibodies. Furthermore, the L. lactis-ntATX-D2 vaccinated turkeys had significantly reduced expression of pro-inflammatory cytokine (Interleukin-1β, IL-6 or Interferon-γ) genes in the skin, muscle, spleen and cecal tonsil tissues when compared to unvaccinated and C. septicum-challenged control group. Our findings show that a L. lactis-based oral recombinant vaccine expressing ntATX-D2 of C. septicum alpha-toxin can provide protective immunity against CD in turkeys, and thus providing a novel scope for devising probiotic-based oral vaccines against important Clostridial diseases in poultry.