Effect of Intestinal Flora on Megaenteron of Mice

Abstract

AbstractCF#1 germfree (GF) and conventional (CV) mice as well as offspring of conventionalized GF (GF‐CV) mice were orally inoculated with Escherichia coli 0115a, c: K(B), a causative agent of megaenteron in mice. Although CV and GF mice showed no clinical signs and survived, all of the GF‐CV mice died with diarrhea by day 14 after inoculation. Thickened wall of the large intestine, microscopically showing proliferation of crypt type cells, was seen in GF and GF‐CV mice but not in CV mice. In addition, in GF‐CV mice, hemorrhage and severe erosion with marked inflammatory reactions were observed. While the inoculated E. coli could not colonize in CV mice, a level of 108 cells/g feces was maintained in GF mice from day 1 after inoculation to the end of examination (on day 28) and in GF‐CV mice from day 5 to the time of death. Newly prepared germfree (GF‐CV‐GF) mice obtained hysterectomy from GF‐CV mice showed a low sensitivity as comparable to that in GF mice. On the other hand, ex‐germfree mice produced by oral administration of feces of GF‐CV mice showed severe infection as comparable to that seen in GF‐CV mice. These results suggest that the intestinal flora may play roles both on protecting from the infection of pathogenic E. coli and on enhancing the infection.