Protective effect of bifidus milk on the experimental infection with Salmonella enteritidis subsp. typhimurium in conventional and gnotobiotic mice

The ability of Bifidobacterium bifidum from a commercial bifidus milk to an tagonize Salmonella enteritidis subsp. typhimurium In vivo, and to reduce t he pathological consequences for the host, was determined using conventiona l and gnotobiotic mice. Conventional animals received daily, by gavage, 0.1 ml bifidus milk containing about 10(9) cfu B, bifidum and germ-free animal s received a single 0.1 ml dose. The conventional and gnotobiotic groups we re challenged orally with 10(2) cfu of the pathogenic bacteria 5 and/or 10 d after the beginning of treatment. Control groups were treated with milk. Bifidus milk protected both animal models against the challenge with the pa thogenic bacteria, as demonstrated by survival and histopathological data, However, to obtain the protective effect in gnotobiotic animals, the treatm ent had to be initiated 10 d before the challenge. In experimental and cont rol gnotobiotic mice, Salm. enteritidis subsp. typhimurium became similarly established at levels ranging from 10(8) to 10(9) viable cells g(-1) of fa eces and remained at these high levels until the animals died or were sacri ficed. It was concluded that the protection against Salm, enteritidis subsp , typhimurium observed in conventional and gnotobiotic mice treated with bi fidus milk was not due to the reduction of the intestinal populations of th e pathogenic bacteria.