NMR DETECTION OF (CH3COOH)-C-13-C-13 FROM 3-C-13-GLUCOSE - A SIGNATURE FOR BIFIDOBACTERIUM FERMENTATION IN THE INTESTINAL-TRACT

The gastrointestinal tracts of breast-fed infants are colonized more e asily with bifidobacteria than are those of formula-fed infants. Colon ization is thought to reduce infant diarrhea. Amendments to formulas t hat improve colonization by bifidobacteria are being actively investig ated. Colonization studies almost invariably require measurements of t he concentration of the bifidobacteria in feces to assess their import ance in the colon. We investigated the use of nuclear magnetic resonan ce (NMR) analysis of products of fermentations of 1- and 3-C-13-glucos e to evaluate the importance of bifidobacteria in the colonic ecosyste m. Bifidobacteria use a unique pathway of hexose catabolism to produce primarily acetate and lactate. The fermentation yields 3 mol of aceta te from 2 mol of glucose. Two of the acetates are formed from C1 and C 2 of glucose and the third is formed entirely from C3 of glucose. We f irst employed high resolution NMR to verify the pathway used by a pure culture of Bifidobacterium bifidum. The major products of fermentatio n of 1- and 3-C-13-glucose were acetate and lactate. Most of the C-13 from 3-C-13-glucose was in (CH3)-C-13 (COOH)-C-13 with equal enrichmen t in the methyl and carboxyl groups. The C-13-acetate from 1-C-13-gluc ose was almost entirely enriched in the methyl of acetate and no (CH3C OOH)-C-13-C-13 was produced. NMR analysis of glucose fermentation by t he colonic flora of a 158-d-old strictly breast-fed infant showed prod uction of (CH3COOH)-C-13-C-13 from 3-C-13-glucose. The amount of (CH3C OOH)-C-13-C-13 formed established that the Bifidobacterium pathway was the major pathway used for glucose fermentation by this infant's colo nic microbes.