ORIGINAL PAPER M. Gmeiner á W. Kneifel á K. D. Kulbe á R. Wouters P. De Boever á L. Nollet á W. Verstraete In¯uence of a synbiotic mixture consisting of Lactobacillus acidophilus 74-2 and a fructooligosaccharide preparation on the microbial ecology sustained in a simulation of the human intestinal microbial ecosystem (SHIME reactor) Received: 22 January 1999 / Received revision: 13 July 1999 / Accepted: 13 August 1999 Abstract Lactobacillus acidophilus 74-2, which is used in probiotic products, was administered, with fructo- oligosaccharide in a milk-based product, to the second vessel (duodenum/jejunum) of the SHIME reactor, an in vitro simulation of the human intestinal microbial ecology. The main focus of this study was to monitor the changes of the population density of selected bacterial species in the intestine and the changes of metabolic activities during the supplementation of L. acidophilus and fructooligosaccharide in the SHIME reactor. Interestingly, the addition of L. acidophilus 74-2 with fructooligosaccharide gave rise to an increase of bi®do- bacteria. Moreover, major positive changes occurred in the production of volatile fatty acids: a strong upward trend was observed especially in the case of butyric acid and propionic acid. Furthermore a noticeable increase of b-galactosidase activity was monitored, while the activity of b-glucuronidase, generally considered unde- sirable, declined. Introduction The gastrointestinal tract of a single individual harbours about 400 dierent species of bacteria. These large and diverse populations mediate the digestive functions of the human colon (Finegold et al. 1983; Holdeman et al. 1976). A variety of fermentation products in¯uence the anatomy, physiology and immunology of the host and conversely the general constitution of the host aects the microbial community in the intestine. Hence, regional dierences occur in bacterial activities in the colon and, since the intestine is not easy to access, investigations are carried out in vitro by simulating the dierent parts of the gastrointestinal tract with multi-stage culture sys- tems (Miller and Wolin 1981; Veilleux and Rowland 1981; Gibson et al. 1988; Macfarlane et al. 1989). In this context, a simulation of the human intestinal microbial ecosystem (SHIME) was developed to study the diverse microbial community of the intestinal tract (Molly et al. 1993). Diet plays a major role in the composition of the hu- man gut microbiota. Evidence is presented that a sup- plementation of probiotic strains at a dose level of 10 8 ±10 9 cfu per head causes signi®cant changes in an established gastrointestinal bacterial community. These conversions comprise alterations in bacterial populations and dierent biochemical activities. Recent advances in probiotic re- search have revealed a relationship between the ingestion of probiotic products and symptomatic relief of gastro- intestinal disorders such as diarrhoea (Isolauri et al. 1991; Siitonen et al. 1990; Beck and Necheles 1961) and con- stipation (Seki et al. 1978). Other clinical studies have indicated the cholesterol-assimilating activity of dierent probiotic strains in vitro (Lin et al. 1989; Gilliland et al. 1985; Rasic et al. 1992) and the role of Lactobacillus and Bi®dobacterium strains on cancer suppression (Marteau et al. 1990) by alterations of faecal bacterial enzymes, which are positively related to colon cancer development (Goldin and Gorbach 1984; Goldin et al. 1980). While clinical research has progressed, there have been developments in the application of probiotic bac- terial strains to new food products, including fermented cereals, infant formulas and therapeutic foods, in addi- tion to their application to dairy products. Relatively new functional food ingredients are oligosaccharides, which provide useful modi®cations to Appl Microbiol Biotechnol (2000) 53: 219±223 Ó Springer-Verlag 2000 M. Gmeiner á W. Kneifel Department of Dairy Research and Bacteriology, University of Agriculture, Gregor Mendel-Straûe 33, A-1180 Vienna, Austria K. D. Kulbe Institute of Food Technology, University of Agriculture, Muthgasse 18, A-1190 Vienna, Austria R. Wouters á P. De Boever á L. Nollet á W. Verstraete (&) Laboratory of Microbial Ecology, Faculty of Agricultural and Applied Biological Science, University of Gent, Coupure Links 653, B-9000 Gent, Belgium e-mail: willy.verstraete@rug.ac.be Tel.: +32-9-264-59-76 Fax: +32-9-264-62-48