Evaluation of long-term immune response in cattle to botulism using a recombinant E. coli bacterin formulated with Montanide™ ISA 50 and aluminum hydroxide adjuvants.

Botulism is a severe disease caused by potent botulinum neurotoxins (BoNTs) produced by Clostridium botulinum. This disease is associated with high-lethality outbreaks in cattle, which have been linked to the ingestion of preformed BoNT serotypes C and D, emphasizing the need for effective vaccines. The potency of current commercial toxoids (formaldehyde-inactivated BoNTs) is assured through tests in guinea pigs according to government regulatory guidelines, but their short-term immunity raises concerns. Recombinant vaccines containing the receptor-binding domain have demonstrated potential for eliciting robust protective immunity. Previous studies have demonstrated the safety and effectiveness of recombinant E. coli bacterin, eliciting high titers of neutralizing antibodies against C. botulinum and C. perfringens in target animal species. In this study, neutralizing antibody titers in cattle and the long-term immune response against BoNT/C and D were used to assess the efficacy of the oil-based adjuvant compared with that of the aluminum hydroxide adjuvant in cattle. The vaccine formulation containing Montanide™ ISA 50 yielded significantly higher titers of neutralizing antibody against BoNT/C and D (8.64 IU/mL and 9.6 IU/mL, respectively) and induced an immune response that lasted longer than the response induced by aluminum, extending between 30 and 60 days. This approach represents a straightforward, cost-effective strategy for recombinant E. coli bacterin, enhancing both the magnitude and duration of the immune response to botulism.

Immunogenicity of a Bivalent Non-Purified Recombinant Vaccine against Botulism in Cattle.

Botulism is a potentially fatal intoxication caused by botulinum neurotoxins (BoNTs) produced mainly by Clostridium botulinum. Vaccination against BoNT serotypes C and D is the main procedure to control cattle botulism. Current vaccines contain formaldehyde-inactivated native BoNTs, which have a time-consuming production process and pose safety risks. The development of non-toxic recombinant vaccines has helped to overcome these limitations. This study aims to evaluate the humoral immune response generated by cattle immunized with non-purified recombinant fragments of BoNTs C and D. Cattle were vaccinated in a two-dose scheme with 100, 200 and 400 µg of each antigen, with serum sampling on days 0, 56, 120, and 180 after vaccination. Animals who received either 200 or 400 µg of both antigens induced titers higher than the minimum required by the Brazilian ministry of Agriculture, Livestock and Food Supply and achieved 100% (8/8) seroconversion rate. Animals vaccinated with commercial toxoid vaccine had only a 75% (6/8) seroconversion rate for both toxins. Animals that received doses containing 400 µg of recombinant protein were the only ones to maintain titers above the required level up until day 120 post-vaccination, and to achieve 100% (8/8) seroconversion for both toxins. In conclusion, 400 µg the recombinant Escherichia coli cell lysates supernatant was demonstrated to be an affordable means of producing an effective and safe botulism vaccine for cattle.