The derivation and use of mice which do not harbour lactobacilli in the gastrointestinal tract.

Penicillin treatment used in conjunction with germfree technology has allowed the derivation of a colony of BALB/c mice which do not harbour lactobacilli in the gastrointestinal tract. The animals continue to harbour Gram-negative anaerobes and coliforms, but not enterococci or filamentous segmented ileal microbes. Isolates of lactobacilli from rodents were able to colonize the gastrointestinal tract of the mice; and isolate from a fowl could not establish in these animals.