Effect of Bovine or Human Milk on the Establishment of Bifidobacterium bifidum and Some Other Bacteria from the Human Neonatal Microflora in Gnotobiotic Mice

A strain of Bifidobacterium bifidum which was dependent on bifidus factors was administered to four groups of germ-free mice each receiving a different sample of human milk containing the same concentration of bifidus factors. The strain became established in three of the four groups in numbers varying between 5 ± 107 and 1 ± 1010/g faeces. B.bifidum also became established in numbers varying between 5 ± 109 and 2 ± 1010/g faeces in mono-associated mice receiving diets containing little or no bifidus factors. The caeca of all the germ-free mice examined contained bifidus factors in higher concentrations than in human milk. This concentration decreased in mice where B.bifidum was established. Thus, no relation was observed between the dietary concentration of bifidus factors and the faecal levels of B.bifidum. In addition, no antagonism was observed between B.bifidum and an Escherichia coli strain, a Klebsiella pneumoniae strain and a Bacteroides sp. strain, all isolated from the stools of newborn babies, although the caecal pH of mice receiving human milk fell to 5.2.