Background: Probiotic bacteria have a beneficial effect on intestinal inflammation. In this study, we have examined the effect of lactic acid and commensal Gram positive (+) bacteria conditioned media (CM) on tumour necrosis factor a (TNF-a) release and the mechanisms involved. Methods: Lipopolysaccharide (LPS) induced TNF-a secretion by peripheral blood mononuclear cells or the THP-1 cell line was monitored in the presence or absence of bacteria CM obtained from two probiotic strains, Bifidobacterium breve (Bb) and Streptococcus thermophilus (St), and three commensal bacterial strains (Bifidobacterium bifidum, Ruminococcus gnavus, and unidentified Streptococcus). Bb and St bacteria CM were allowed to cross filter grown intestinal epithelial cell monolayers (HT29-19A) to assess intestinal transport of active bacterial products. These products were characterised and their effect on LPS binding to THP-1 cells and nuclear factor kB (NFkB) activation assessed. Results: Dose dependent inhibition of LPS induced TNF-a secretion was noted for both probiotic bacteria CM (64% and 71% inhibition for Bb and St, respectively) and to a lesser extent commensal bacteria CM (21-32% inhibition). Active products from Bb and St were resistant to digestive enzymes and had a molecular mass ,3000 Da. Their inhibitory effect was preserved after transepithelial transport across intestinal cell monolayers, mainly in inflammatory conditions. LPS-FITC binding to THP-1 cells and NFkB activation were significantly inhibited by Bb and St CM. Conclusion: B breve and S thermophilus release metabolites exerting an anti-TNF-a effect capable of crossing the intestinal barrier. Commensal bacteria also display a TNF-a inhibitory capacity but to a lesser extent. These results underline the beneficial effect of commensal bacteria in intestinal homeostasis and may explain the role of some probiotic bacteria in alleviating digestive inflammation.

(Gut 1998;42:538-545)

Current prebiotics, such as fructo-oligosaccharides (FOS), are limited in their persistence in the distal colon and are predominantly fermented in the proximal colon. In order to identify a potential alternative, the differences in the fermentation profile of arabinogalactan (AG) and FOS have been assessed in the Simulator of the Human Intestinal Microbial Ecosystem. The effect of each product on the composition and activity of the microbial community was analysed during a 3-week treatment period at a dose of 5 g day(-1). While FOS indeed was mainly fermented in the simulated proximal colon, AG was still available for fermentation in the simulated distal colon as shown by pH profiles, size exclusion chromatography and analyses of specific enzymatic activities. As a consequence, the main effect of the products (increase in propionate and butyrate and decrease in ammonium production) occurred in different intestinal areas. DGGE and qPCR analyses confirmed that the main modulation of the microbiota by the two products occurred in different areas of the gut. AG was associated with a statistically significant increase in the concentration of total bacteria, Bacteroidetes, Faecalibacterium prausnitzii, a delayed bifidogenic effect and a decrease of the pathogenic Clostridium perfringens. FOS led to a strong lactobacillogenic effect.

The intestinal barrier capacity to milk proteins seems to be reinforced by dehydrated fermented milk, but milk and fermented milks are equally efficient in inducing cow's milk allergy in guinea pigs.