Susceptibility of germ-free mice to infectious megaenteron.

Germ-free (GF)-ICR mice were shown to be less susceptible to oral inoculation with a pathogenic strain of Escherichia coli (E. coli 0115a, c: K(B) than GF-CF No.1 mice. In GF-CF No. 1 mice a large number of organisms were recovered from the intestinal wall from the cecum to the rectum 3 to 7 days after inoculation. Unlike those in GF-CF No. 1 mice, lesions in GF-ICR mice were localized in a part of the cecum and organisms were recovered only from the cecal wall and rarely from organs other than those of the alimentary tract. In both strains of mice, however, organisms were recovered in large number from the intestinal contents. Histopathology and immunofluorescence revealed organisms closely attached to the surface of the cecum, colon and rectal epithelia in GF-CF No. 1 mice but only in a part of the cecal epithelium in GF=ICR mice. After being in contact with conventional CF No. 1 mice for 21 days and then inoculated orally with the pathogenic E. coli, ex GF-CF No. 1 mice died within 14 days with severe intestinal lesions, but ex-GF-ICR mice survived without lesions.