The etiology of transmissible murine colonic hyperplasia.

The etiology of a transmissable colonic mucosal hyperplasia of mice was investigated. Hyperplasia was produced in mice inoculated with unfiltered colonic suspension from affected mice, but infectivity was lost after passage through a 0.45 mum filter. The etiologic agent was subsequently identified as a variant of Citrobacter freundii. The organism induced colonic mucosal hyperplasia when inoculated into germfree mice, and it was recovered in pure culture from the affected animals.