Association of Salmonella typhimurium with, and its invasion of, the ileal mucosa in mice.

A wild-type strain of Salmonella typhimurium and three mutant rough colonial variants of the wild type were compared for their ability to become associated with and invade the ileal mucosa of germfree and specific-pathogen-free mice. The rough-mutant strains differed from the wild type in having incomplete lipopolysaccharides lacking one or more sugars in the polysaccharide moiety. The wild-type and mutant strains also differed one from the other in the types of appendages (flagella, pili) on their surfaces. Depending upon the dosage of bacteria given, all mutant strains as well as the wild type could associate with and invade the intestinal mucosa of infected gnotobiotic mice. If the infecting dosage was high enough, at least two of the mutant strains and the wild type invade the intestinal mucosa of the specific-pathogen-free animals. O antigen, flagella, or pili do not appear to be essential for the association of S. typhimurium with the mucosal surface of the mouse ileum. O antigen on the bacterial cell surface may be important, but not essential, for invasion of the ileal mucosa.