Growth of Salmonellae in Orally Infected Germfree Mice

Germfree mice were infected intragastrically, intravenously, or intraperitoneally with 10(3) to 10(9) viable Salmonella typhi Ty2, S. gallinarum 9240, or S. enteritidis 5694. The 50% lethal doses were compared with those for conventionally raised mice. Substantial growth of the salmonellae occurred in the intestinal tract of the germfree mice but, despite the presence of more than 10(9) viable S. typhi or S. gallinarum in the lumen, the liver and spleen cultures remained Salmonella-free, and all of the mice survived the oral challenge. The ileal and cecal Peyer's patches and the mesenteric lymph nodes of these mice contained 10(3) to 10(4) viable salmonellae within 24 h of introduction of the inoculum into the stomach. Despite this local involvement, the infection did not spread systemically even when host resistance was reduced by means of sublethal, whole-body gamma irradiation before oral challenge. Germfree mice infected orally with as few as 10 mouse-virulent S. enteritidis quickly developed severe diarrhea and died within 5 to 8 days as a result of a spreading systemic disease.