Cleavage of L-leucine-containing dipeptides by Clostridium butyricum.

The ability of Clostridium butyricum cultures to hydrolyze three L-leucine-containing dipeptides (Leu-Leu, Leu-Gly and Gly-Leu) in a synthetic minimal medium is demonstrated by using gas chromatography coupled with mass spectrometry. The 13C nuclear magnetic resonance and a labeled dipeptide L-[1-13C]Leu-Gly were used to confirm this activity.

Oligofructose contributes to the protective role of bifidobacteria in experimental necrotising enterocolitis in quails.

Bifidobacteria are dominant in the gut of full-term infants, although colonisation by them is often delayed in preterm neonates. Bifidobacteria are recognised to have beneficial effects on digestive disorders and they might prevent neonatal necrotising enterocolitis (NEC), a gastrointestinal disease that predominantly affects premature infants. They have been shown to protect gnotobiotic quails against NEC-like lesions when the birds were inoculated with faecal flora from preterm infants, decreasing the clostridial population. The present study was designed to investigate whether oligofructose, which stimulates the activity of bifidobacteria, may enhance their protective role. Experiments were done in eight groups of germ-free quails for 28 days. The groups differed as to their bacterial status, diet and environment. Quails were inoculated with one of two flora from premature twins. The first flora included Bifidobacterium pseudo-catenulatum, Escherichia coli and no clostridia. The second flora included clostridial species and was associated with B. infantis-longum. Caecal bacterial population and metabolism changes were investigated with a lactose (6%) diet versus a lactose-oligofructose (3%-3%) diet, either in a gnotobiotic environment or in an ordinary environment permitting post-colonisation by exogenous bacteria. In both environments and with both flora, oligofructose significantly increased the level of bifidobacteria and this was associated with a decrease of E. coli or C. perfringens and C. ramosum. The bacterial changes in the ordinary environment depended on the initial composition of the microflora and the colonisation resistance against exogenous bacteria was more efficient with the flora that included B. pseudo-catenulatum. The changes in caecal pH and short-chain fatty acids were minimal. It was demonstrated that, irrespective of the environmental conditions, the use of oligofructose helped to prevent the overgrowth of bacteria implicated in necrotising enterocolitis in preterm neonates.

Clostridial pathogenicity in experimental necrotising enterocolitis in gnotobiotic quails and protective role of bifidobacteria.

The pathogenesis of neonatal necrotising enterocolitis (NEC) remains unclear. Gnotobiotic quails fed a lactose diet have been used to investigate the role of clostridial strains originating from faecal specimens of neonates through the intestinal lesions, the changes in microflora balance and the production of bacterial metabolites, i.e., short-chain fatty acids and hydrogen. Bifidobacteria are thought to exert various beneficial effects on host health, including interaction with the colonic microflora. Therefore, it was hypothesised that a protective role could be exercised through bifidobacterial colonisation. A Clostridium butyricum strain (CB 155-3) and a whole faecal flora including three clostridial species (C. butyricum, C. perfringens, C. difficile), each from premature infants suffering from NEC, caused caecal lesions in quails similar to those observed in man, i.e., thickening of the caecal wall with gas cysts, haemorrhagic ulceration and necrotic areas. Conversely, a whole faecal flora including bifidobacteria (identified as Bifidobacterium pseudo-catenulatum) and no clostridia, isolated from a healthy premature infant, was unable to produce NEC-like lesions. When the two clostridial groups were associated with a Bifidobacterium strain (B. infantis-longum, CUETM 89-215, isolated from a healthy infant), bifidobacterial colonisation suppressed all pathological lesions. This study is the first demonstration of a protective role for bifidobacteria against NEC via the inhibition of growth of C. butyricum or the disappearance of C. perfringens. C. difficile was not found to be responsible for the aetiology of the caecal lesions in quails. The main effect of bifidobacteria on lactose fermentation was either a dramatic decrease or a disappearance of butyric acid. The protective role was not associated with changes in H2 production. Therefore, a new step between colonic colonisation and its relevance to NEC is thought to involve the fermentation of unabsorbed lactose into butyric acid at the onset of the disease.