Immunogenicity of a pentavalent recombinant Escherichia coli bacterin against enterotoxemia and botulism in sheep.

Producing commercial bacterins/toxoids against Clostridium spp. is laborious and hazardous. Conversely, developing prototype vaccines using purified recombinant toxoids, though safe and effective, is both laborious and costly for application in production animals. Considering that inactivated recombinant Escherichia coli (bacterin) is a simple, cost-effective, and to be safe solution, we evaluated, for the first time, a pentavalent formulation of recombinant bacterins containing the alpha, beta, and epsilon toxins of Clostridium perfringens and C and D neurotoxins of Clostridium botulinum in sheep. Subcutaneously, 18 Texel sheep received two doses (200 μg of each antigen) of recombinant bacterin (n=7) or purified recombinant antigens (n=6) on days 0 and 28, while the control group (n=5) did not receive an immunization. Sera samples from days 0 (before the 1st dose), 28 (before the 2nd dose), and 56, 84, and 112 were used for measuring IgG (indirect ELISA) and neutralizing antibodies (mouse serum neutralization). Both formulations induced significant levels of IgG against all five toxins (p<0.05) up to day 112, with peaks at days 28 and 56 post-immunization. The expected booster effect occurred only for the botulinum toxins. The neutralizing antibody titers were satisfactory against ETX (≥ 2 IU/ml for both formulations) and BoNT-D [5 IU/ml (bacterin) and 10 IU/ml (purified)]. While adjustments are required, the recombinant bacterin platform holds great potential for polyvalent vaccines due to its straightforward, safe, and cost-effective production, establishing it as a user-friendly technology for the veterinary immunobiological industry.

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Declaration of Competing Interest ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: