Potency testing of Clostridium septicum bacterins in sheep and laboratory animals

The immunogenic potency of bacterins containing Clostridium septicum was evaluated in mice, hamsters, guinea pigs, rabbits and sheep to establish potency requirements for these bacterins. Two subcutaneous injections of Cl. septicum bacterins were shown to provide resistance against intramuscular spore challenge. Protection in mice, hamsters and guinea pigs was generally at low levels, in the range of 1 to 5 LD50. Efficacy estimates, at these levels of challenge, indicated that a degree of relationship existed between the response of rabbits and the response of sheep. This relationship was confirmed at higher levels of spore challenge, at greater than 5 to 500 LD50. Undiluted bacterins were classed as good or poor based on percent survival responses in sheep. Bacterins providing 90 to 100% survival were classed as good; those providing 30 to 57% survival were classed as poor. In rabbits, this classification was less evident with the undiluted bacterins. Dilution of bacterins to 1:32 provided a discriminatory level with 7 of 8 bacterins examined and represented correlation of the sheep and rabbits responses. A similar relationship was demonstrated between protection in sheep against spore challenge and the antitoxin response in rabbits to undiluted bacterins. Antitoxin responses, when obtained, were generally higher in rabbits than those obtained in sheep. Further evaluation of a good and a poor bacterin in rabbits indicated that no direct relationship existed between antitoxin titer in rabbits and resistance to spore challenge, when compared at the same dilutions of bacterins. Evaluation of serum agglutination responses to types I and II somatic antigens indicated a poor relationship between agglutination response and resistance to spore challenge in both sheep and rabbits. Cl. septicum toxoids were shown to provide resistance to spore challenge in rabbits.