DEGRADATION AND FERMENTATION OF ALPHA-GLUCO-OLIGOSACCHARIDES BY BACTERIAL STRAINS FROM HUMAN COLON - IN-VITRO AND IN-VIVO STUDIES IN GNOTOBIOTIC-RATS

The ability of several human gut bacteria to break down alpha-1,2 and alpha-1,6 glycosidic linkages in alpha-gluco-oligosaccharides (GOS) wa s investigated in vitro in substrate utilization tests. Bacteroides th etaiotaomicron, Bifidobacterium breve and Clostridium butyricum, which are usually found in the infant gut and have been associated with bot h beneficial and deleterious effects on health, were studied. alpha-Gl uco-oligosaccharide degradation was compared in vitro and in vivo in g notobiotic rats associated with these organisms, inoculated alone or i n combination. Oligomer breakdown and short chain fatty acid and gas p roduction indicated hydrolysis and fermentation of the substrate. In v itro and in vivo, Cl. butyricum was the least efficient in utilizing G OS, whereas Bact. thetaiotaomicron was the most efficient. Kinetic stu dies on GOS hydrolysis in pH-regulated fermenters showed that alpha-1, 2 glucosidic bonds, which characterize the substrate, were more resist ant than alpha-1,6 linkages. Adaptation of gnotobiotic rats to a diet containing 2% (w/w) GOS significantly increased the hydrolysis of alph a-1,2 glucosidic bonds. Combination of bacteria in trixenic rats impro ved GOS degradation and inhibited Cl. butyricum metabolism. This inhib ition was confirmed in pH-regulated fermenters containing GOS as the p rincipal carbon source. The association of beneficial bacteria and GOS may therefore have a potential health-promoting effect in human neona tes.