Botulism in metronidazole- treated conventional adult mice challenged orogastrically with spores of Clostridium botulinum type A or B.

Conventional adult mice were pretreated with metronidazole to make their intestinal tracts receptive to colonization by Clostridium botulinum. These mice, in groups of 10, were fed 0 (controls), 10(2), 10(3), 10(4), or 10(5) C. botulinum type B spores and were placed for observation in filter-lid cages whose screen floors minimized the amounts of feces available for coprophagy. The opportunity to eat feces was made equal for all mouse groups by placing one mouse of every group in each of 10 cages. Mice given a spore inoculum began to develop botulism after incubation periods of slightly less than 2.75 days. Morbidity rates, which reached maxima within 5 days of challenge, were related to inocula levels. Mortality rates were also dose related. Mice given 10(5) spores and then type B antitoxin intraperitoneally, a treatment not affecting intraintestinal toxin production, remained healthy. Morbidity among control mice was seldom more than 10% and could be ascribed to toxin ingested with feces. A C. botulinum type A spore suspension gave similar results, although morbidity and mortality rates were generally lower than after challenge with a comparable number of type B spores. Mice challenged with 10(2) or 10(5) spores had similar toxin levels in their large intestines 48 h later. Morbidity rates correlated better with toxin levels in the small intestines.