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Aims: To investigate the effects of whey retentate from Bi®dobacteria fermented milk. Methods and Results: The simulator of the human intestinal microbial ecosystem (SHIME) was used. The composition of the microbiota and its metabolic activities were analysed. Changes in the microbial composition became apparent within 15 days of the treatment in the vessels representing the ileum and the large intestine. The whey retentate favoured the growth of endogenous bi®dobacteria and induced a decrease in Bacteroides fragilis and in sul®pho-reducing clostridia, especially Clostridium perfringens. After the administration was stopped, these populations tended to revert to their original levels, except for the streptococci and the staphylococci populations. The treatment also led to an increase in acetic acid, CH 4 and CO 2 production, suggesting overgrowth of some anaerobic bacteria. Ammonium, generally considered as undesirable, declined. Conclusions: The whey retentate clearly altered the microbial community in the SHIME. Signi®cance and Impact of the Study: Whey retentate appears to exert a bene®cial effect on the in vitro gastrointestinal system; these ®ndings warrant con®rmation by in vivo studies.

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The vernacular name ' fluorescent Pseudomonas group 97-514 ' was coined for a group of 43 strains isolated from two French natural mineral waters. All these strains were Gram-negative, rod-shaped and motile by means of a single polar flagellum. They produced fluorescent pigment (pyoverdin) on King B medium, catalase and cytochrome oxidase. They were capable of respiratory but not fermentative metabolism. They were not able to accumulate poly-β-hydroxybutyrate and possessed an arginine dihydrolase system. DNA-DNA relatedness studies (S1 nuclease method) showed that the 43 strains of ' fluorescent Pseudomonas group 97-514 ' formed a genetically homogeneous group (DNA-DNA relatedness ranged from 70 to 100 %). A total of 76 strains representing well-known or partially characterized species of the genus Pseudomonas sensu stricto had 7-56 % DNA hybridization with strain CFML 97-514