Bacterial flora of ex-germfree mice after oral inoculation of feces from various species of conventional animals.

Emulsions of fresh feces from a conventional mouse, rabbit, dog or cynomolgus monkey were administered orally to germfree and conventional ICR mice. Various fecal floras bearing a striking resemblance in pattern to those in the inoculant became established in the inoculated ex-germfree mice. Reinoculation of these ex-germfree mice with fecal emulsions from a conventional mouse made 21 days after the original inoculation (conventionalization) led to alteration of their floras to the indigenous pattern of conventional mice. The administration of feces from the conventional animals of different species did not appreciably modify the fecal flora of conventional mice. The results indicate that intestinal flora of animals is determined in the first stage by that of the contaminants, but this would be altered later under the predominant influence of the various host factors.