Expression of HC subunits from Clostridium botulinum types C and D and their evaluation as candidate vaccine antigens in mice.

Two proteins representing the heavy-chain subunits of botulinum neurotoxin types C and D were expressed in Escherichia coli, and their vaccine potential was evaluated. Mice were vaccinated with doses ranging from 0.5 to 10 microg and were challenged with 10 to 10(5) 50% lethal doses of toxin. For the type C subunit protein, C50, two doses of 2 microg were required for full protection, while, for type D subunit protein, D50, two 1- microg doses were required. A bivalent vaccine consisting of a mixture of these two proteins also provided protection against both botulinum neurotoxin type C and type D challenge. Antibody levels in serum were determined by both enzyme-linked immunosorbent assays and serum neutralization assays