Microbial interference and colonization of the murine gastrointestinal tract by Listeria monocytogenes

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Abstract
Two strains of L. monocytogenes, 1 that formed smooth colonies on agar surfaces and a variant of it that formed rough colonies, colonized the gastrointestinal tracts of germfree mice. Within 24 h after mice were inoculated orally with about 100 bacteria, the population levels per gram (wet weight) of tissue of both strains were 105-107 in the stomach and ileum and 108-109 in the cecum and colon, respectively. As detected in Gram-stained histological sections, in such gnotobiotes, the bacteria colonized the lumen in all areas of the tract and much of the mucus layer on the epithelial surface in the proximal colon. The strain that formed smooth colonies did not colonize the tracts of specific-pathogen-free mice, but did colonize, to the same levels as in germfree mice, the stomachs and bowels of ex-germfree mice previously associated with 2 members of the indigenous flora (Bacteroides and Clostridium). In the latter animals, the listeria did not form layers on the colonic epithelium as efficiently as they did in monoassociated gnotobiotes.