Antagonistic effect of extremely oxygen sensitive clostridia from the microflora of conventional mice and of Escherichia coli against Shigella flexneri in the digestive tract of gnotobiotic mice

Abstract

Two extremely oxygen-sensitive strains of Clostridium sp., designated Clostridium E and P, were obtained from digestive microflora of conventional mice and found to constitute a barrier against S. flexneri SF-2 when associated in vivo with E. coli K-12. These and other simplified fractions of the conventional microflora were demonstated to have an effect comparable to that of the total flora. When K-12 and Clostridium E were established in gnotobiotic mice before the introduction of SF-2, the latter was reduced to a level below detection in the digestive tract. When SF-2 was established first, the antagonistic effect exerted by Clostridium E and K-12 was variable and, apparently, related to the rate of establishment of Clostridium E. Mutants of SF-2 resistant to the barrier effect of Clostridium E and K-12 appeared at the end of 3 months when SF-2 was established in gnotobiotic mice alone or with K-12, and after only a week when SF-2 was associated only with Clostridium E. These results suggest that the bacterial antagonism in this model is related to the production in vivo of an antibiotic substance active against SF-2. It appears that the substance may be produced by Clostridium E, stimulated by K-12.