Intraintestinal toxin in infant mice challenged intragastrically with Clostridium botulinum spores

Conventionally raised suckling mice were injected intragastrically with 10(5) spores of a Clostridium botulinum type A culture. Botulism was not observed, but 80% or more of mice challenged when 8 to 11 days old had botulinum toxin in the large intestine 3 days later. Mice younger than 7 days or older than 15 days were resistant to the challenge. When in vivo toxin production was started by spores given to 9-day-old mice, toxin was present in the intestine at 1 through 7 days postchallenge but with greatest consistency between 1 and 4 days. Total toxin in an intestine ranged up to 1,920 50% lethal doses as titrated intraperitoneally in adult mice. The dose infecting 50% of a group of 9-day-old mice was 700 (95% confidence limits of 170 to 3,000) spores per animal. Toxin was formed in the lumen of the large intestine; it was not associated with the ileum. Injection of 10(5) spores intraperitoneally into 9-day-old mice resulted in toxin production in the large intestines of 30% of the test animals.