Effect of ingestion of green seaweed, Ulva lactuca, (70 g kg−1) during a 6-week period on caecal and colonic mucosas was studied in germ-free (GF) rats and in heteroxenic (HE) rats harbouring a human bacterial flora (GF rats associated with a human flora). The pH and sulphide concentration of the caecal contents, crypt morphometry, mitotic index and mucin types in the caecal and distal colonic mucosas were determined. In the GF caecum, Ulva strongly increased crypt depth and mucin-containing cells irrespective of the mucin type studied (neutral, acidic or sulphated) compared to the control diet but had no significant effect on mitotic index. The crypt depth and mucin-containing cells in the caecum were higher in HE than in GF control rats. They were slightly but significantly increased by Ulva. In the distal colon mucosa of GF rats, Ulva decreased crypt depth and cell number as well as sulphomucin-containing cells. Conversely, in the HE rats, it increased crypt depth and reduced the number of neutral mucin-containing cells. These results show that Ulva lactuca exerts an intrinsic effect on mucosal morphometry and on mucin biosynthesis in GF rats. No pathological alteration was observed in the mucosas and no significant modification of the mitotic index or sulphide production was observed in HE rats. © 1999 Society of Chemical Industry

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.

In vivo fermentation of Ulva lactuca was studied in previously germ-free rats inoculated with human flora obtained from non-, low- and high-methane producers (groups NMP, LMP and HMP, respectively), in comparison to germ-free rats. Rats were fed either a control diet or a diet containing 4% of dried Ulva lactuca. Production of metabolites varied according to the flora and diet. Ulva lactuca induced a specific high production of methane in the HMP group. With the three human flora, Ulva diet induced a similar increase in caecal pH. In the NMP and HMP groups, this increase was associated with a fall of lactic acid caecal concentration. In the LMP group it was related to a decrease in the concentration of short-chain fatty acids. Ulva lactuca appeared to be able to regulate the beta-glucuronidase and beta-glucosidase activities, reducing the relatively high levels observed in groups NMP and HMP and increasing the low levels obtained in the LMP group. Results show that, although it was poorly fermented, Ulva induced significant effects on the gut microflora metabolism. The methanogenic status of the human donor appeared to be an important factor. (C) 1998 SCI.