Host-microflora correlations in infant nutrition.

The intestinal microflora represents an enormous cell mass and has a high metabolic capacity. The symbiotic efficacy of these microbes in humans is still a matter of discussion. Of particular interest, from a biogenetic point of view, are potential symbiotic relations between the bifidobacterial microflora and the breast-fed infant. Our group has conducted studies related to this topic; they were aimed at determining the dimension of microbial assimilation by the host. Our studies with 15N-labeled bifidobacteria have shown that the bifidobacterial microflora is capable of upgrading nonessential nitrogen such as urea nitrogen for the synthesis of microbial protein. Oral single pulse labelings with 15N-labeled bifidobacteria were absorbed to approximately 90% and retained in the infant's protein pool to approximately 70%. These findings demonstrate the high intensity of the substrate flow from the microflora to the host. This might become important under conditions of marginal food protein intake or during periods of accelerated growth.