Urea Utilization by the Intestinal Flora, of Infants Fed Motherʼs Milk and a Formula Diet, as Measured with the 15N-Tracer Technique

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Abstract
15N-Incorporation by intestinal bacteria was measured under different feeding conditions in 16 infants after a single oral loading of 165 mg [15N2]urea .cntdot. kg-1 body weight as a tracer. In 5 subjects on a mother''s milk diet, the 15N-excess in the isolated intestinal bacteria was 1.08 (0.17-1.85) atom-%. The mean 15N-excess in the intestinal flora of 5 formula-fed subjects did not differ significantly from these values [0.63 (0.17-1.05) atom-%]. A trend to a higher incorporation of 15N from labeled urea by the intestinal flora was seen in 4-infants, who were adapted to an increased nutritional urea supply on a special formula, containing 14 g of milk protein, 80 g lactose, 36 g fat, and 0.35 g urea .cntdot. L-1. The same observation was made in 2 infants with chronic renal failure. The incorporation of urea N by the putrefactive intestinal flora of infants on a formula diet as well as by the bifidobacterial flora of those on mother''s milk feeding indicates the utilization of urea as a source of bacterial protein and nucleic acid synthesis. The adaptive usage of urea for the bacterial metabolism can be considered as a sign of supportive detoxification by the intestinal flora.

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