Effect of short-chain carbohydrates on human intestinal bifidobacteria and Escherichia coli in vitro

School of Applied Sciences, South Bank University, 103 Borough Road, London SE1 0AA, *Department of Civil Engineering, Technological Institute, Northwestern University, Evanston IL 60201, USA and MRC Microbiology and Gut Biology Group, Level 6, Ninewells Hospital and Medical School, Dundee DD1 9SY Corresponding author: Dr R. Sharp (e-mail: sharp{at}sbu.ac.uk ). Received 17 Jan. 2000; revised version received 19 June 2000; accepted 20 June 2000. Abstract Plate counts and small subunit (SSU) rRNA abundance were used to study the effects of fructo-oligosaccharides (FOS), fructose, or galacto-oligosaccharides (GOS) on bifidobacterial populations in human faecal microbiotas. The bacteria were grown in pH-controlled anaerobic fermentation vessels. Untreated cultures and fructose-amended fermenters were used as controls. Bifidobacterium longum , B. adolescentis and B. angulatum comprised the dominant bifidobacterial populations throughout the experiment. No major differences were found in the four treatments, in terms of viable counts of the organisms or of total populations of bifidobacteria at any time point. However, large differences were observed with respect to the abundance of bifidobacterial SSU rRNA between the treatments. Greatest bifidobacterial SSU rRNA abundance was seen in FOS cultures, with the lowest in the untreated control fermentation. GOS and fructose also increased bifidobacterial SSU rRNA. Cultures supplemented with FOS and GOS were also associated with lower colony counts and SSU rRNA abundance for Escherichia coli , compared with fructose-supplemented and control fermenters. At the 24-h time point, the untreated control contained 19.8 µg of enterobacterial SSU rRNA/ml of culture fluid, compared with 11.4 µg/ml for the fructose fermentation, and 2.6 and 0.5 µg/ml for the FOS and GOS culture vessels, respectively.