Protective potential of recombinant non-purified botulinum neurotoxin serotypes C and D

Botulinum neurotoxin (BoNT) serotypes C and D are responsible for cattle botulism, a fatal paralytic disease that results in great economic losses in livestock production. Vaccination is the main approach to prevent cattle botulism. However, production of commercially available vaccines (toxoids) involves high risk and presents variation of BoNT production between batches. Such limitations can be attenuated by the development of novel nontoxic recombinant vaccines through a simple and reproducible process. The aim of this study was to evaluate the protective potential of recombinant non-purified botulinum neurotoxin serotypes C and D. Bivalent vaccines containing 200 μg rHCC and rHCD each were formulated in three different ways: (1) purified antigens; (2) recombinant Escherichia coli bacterins; (3) recombinant E. coli cell lysates (supernatant and inclusion bodies). Guinea pigs immunized subcutaneously with recombinant formulations developed a protective immune response against the respective BoNTs as determined by a mouse neutralization bioassay with pooled sera. Purified recombinant antigens were capable of inducing 13 IU/mL antitoxin C and 21 IU/mL antitoxin D. Similarly, both the recombinant bacterins and the cell lysate formulations were capable of inducing 12 IU/mL antitoxin C and 20 IU/mL antitoxin D. These values are two times as high as compared to values induced by the commercial toxoid used as control, and two to ten times as high as the minimum amount required by the Brazilian Ministry of Agriculture, Livestock and Food Supply (MAPA), respectively. Therefore, we used a practical, industry-friendly, and efficient vaccine production process that resulted in formulations capable of inducing protective immune response (neutralizing antitoxins) against botulism serotypes C and D.