A cross-sectional study on intestinal microbiota composition was performed on 230 healthy subjects at four European locations in France, Germany, Italy, and Sweden. The study participants were assigned to two age groups: 20 to 50 years (mean age, 35 years; n ‫؍‬ 85) and >60 years (mean age, 75 years; n ‫؍‬ 145). A set of 14 group-and species-specific 16S rRNA-targeted oligonucleotide probes was applied to the analysis of fecal samples by fluorescence in situ hybridization coupled with flow cytometry. Marked country-age interactions were observed for the German and Italian study groups. These interactions were inverse for the predominant bacterial groups Eubacterium rectale-Clostridium coccoides and Bacteroides-Prevotella. Differences between European populations were observed for the Bifidobacterium group only. Proportions of bifidobacteria were two-to threefold higher in the Italian study population than in any other study group, and this effect was independent of age. Higher proportions of enterobacteria were found in all elderly volunteers independent of the location. Gender effects were observed for the Bacteroides-Prevotella group, with higher levels in males than in females. In summary, age-related differences in the microbiota makeup were detected but differed between the study populations from the four countries, each showing a characteristic colonization pattern.

: Delivery mode and feeding method influenced the fecal microbiota of European infants at 6 weeks, as expected, but the effect of country of birth was more pronounced, with dominant bifidobacteria in northern countries and greater early diversification in southern European countries.

Epithelial cells of the mammalian intestine are covered with a mucus layer that prevents direct contact with intestinal microbes but also constitutes a substrate for mucus-degrading bacteria. To study the effect of mucus degradation on the host response, germ-free mice were colonized with Akkermansia muciniphila. This anaerobic bacterium belonging to the Verrucomicrobia is specialized in the degradation of mucin, the glycoprotein present in mucus, and found in high numbers in the intestinal tract of human and other mammalian species. Efficient colonization of A. muciniphila was observed with highest numbers in the cecum, where most mucin is produced. In contrast, following colonization by Lactobacillus plantarum, a facultative anaerobe belonging to the Firmicutes that ferments carbohydrates, similar cell-numbers were found at all intestinal sites. Whereas A. muciniphila was located closely associated with the intestinal cells, L. plantarum was exclusively found in the lumen. The global transcriptional host response was determined in intestinal biopsies and revealed a consistent, site-specific, and unique modulation of about 750 genes in mice colonized by A. muciniphila and over 1500 genes after colonization by L. plantarum. Pathway reconstructions showed that colonization by A. muciniphila altered mucosal gene expression profiles toward increased expression of genes involved in immune responses and cell fate determination, while colonization by L. plantarum led to up-regulation of lipid metabolism. These indicate that the colonizers induce host responses that are specific per intestinal location. In conclusion, we propose that A. muciniphila modulates pathways involved in establishing homeostasis for basal metabolism and immune tolerance toward commensal microbiota.

Although it is well established that early infant feeding has a major influence on the establishment of the gut microbiota, very little is understood about how the introduction of first solid food influences the colonization process. This study aimed to determine the impact of weaning on the faecal microbiota composition of infants from five European countries (Sweden, Scotland, Germany, Italy and Spain) which have different lifestyle characteristics and infant feeding practices. Faecal samples were collected from 605 infants approximately 4 weeks after the introduction of first solid foods and the results were compared with the same infants before weaning (6 weeks of age) to investigate the association with determining factors such as geographical origin, mode of delivery, previous feeding method and age of weaning. Samples were analysed by fluorescence in situ hybridization and flow cytometry using a panel of 10 rRNA targeted group- and species-specific oligonucleotide probes. The genus Bifidobacterium (36.5 % average proportion of total detectable bacteria), Clostridium coccoides group (14 %) and Bacteroides (13.6 %) were predominant after weaning. Similar to pre-weaning, northern European countries were associated with a higher proportion of bifidobacteria in the infant gut microbiota while higher levels of Bacteroides and lactobacilli characterized southern European countries. As before weaning, the initial feeding method influenced the Clostridium leptum group and Clostridium difficile+Clostridium perfringens species, and bifidobacteria still dominated the faeces of initially breast-fed infants. Formula-fed babies presented significantly higher proportions of Bacteroides and the C. coccoides group. The mode of birth influenced changes in the proportions of bacteroides and atopobium. Although there were significant differences in the mean weaning age between countries, this was not related to the populations of bifidobacteria or bacteroides. Thus, although the faecal microbiota of infants after first complementary foods was different to that before weaning commenced, many of the initial influences on microbiota composition were still evident

It was recently found that a mixture of nine amino acids down-regulate Clostridium difficile toxin production when added to peptone yeast extract (PY) cultures of strain VPI 10463 (S. Karlsson, L. G. Burman, and T. Åkerlund, Microbiology 145:1683-1693, 1999). In the present study, seven of these amino acids were found to exhibit a moderate suppression of toxin production, whereas proline and particularly cysteine had the greatest impact, on both reference strains (n ‫؍‬ 6) and clinical isolates (n ‫؍‬ 28) of C. difficile (>99% suppression by cysteine in the highest toxin-producing strain). Also, cysteine derivatives such as acetylcysteine, glutathione, and cystine effectively down-regulated toxin expression. An impact of both cysteine and cystine but not of thioglycolate on toxin yield indicated that toxin expression was not regulated by the oxidation-reduction potential. Several metabolic pathways, including butyric acid and butanol production, were coinduced with the toxins in PY and down-regulated by cysteine. The enzyme 3-hydroxybutyryl coenzyme A dehydrogenase, a key enzyme in solventogenesis in Clostridium acetobutylicum, was among the most up-regulated proteins during high toxin production. The addition of butyric acid to various growth media induced toxin production, whereas the addition of butanol had the opposite effect. The results indicate a coupling between specific metabolic processes and toxin expression in C. difficile and that certain amino acids can alter these pathways coordinately. We speculate that down-regulation of toxin production by the administration of such amino acids to the colon may become a novel approach to prophylaxis and therapy for C. difficile-associated diarrhea.

Objective: To gain an insight into parental perceptions of infant feeding practices in five European countries. Design: An exploratory investigation using focus group discussions. Various aspects addressed included social and cultural setting for the consumption of food, infant feeding practice and behaviour, consumer health awareness and sources of information, and attitudes towards a healthy infant diet. Setting: Focus group participants were recruited from centres in five countries, Germany, Italy, Scotland, Spain and Sweden, with three focus groups being conducted in each centre. Subjects: A total of 108 parents with infants up to the age of 12 months participated in focus group discussions across these centres. Methods: Focus groups were conducted with participants from centres in five countries. Results: The majority of parents in this study chose to initiate breastfeeding and prepare infant food at home. Parents did not strictly adhere to infant feeding guidelines when introducing complementary foods into their infant's diets. There were crosscultural differences in sources of information on infant feeding practice with the paediatrician in Germany, Italy and Spain. The health visitor in Scotland and the child welfare clinics in Sweden were the most popular sources. Conclusions: A number of cultural differences and similarities in attitudes towards infant feeding practice were revealed. This makes European wide approaches to promoting healthy infant feeding difficult as different infant feeding practices are influenced not only by parental perceptions but also by advice from health professionals and feeding guidelines. Further data need to be available on parents' attitudes and beliefs towards infant feeding practice to investigate further the rationale for differing beliefs and attitudes towards infant feeding practice.

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All previously published papers were reproduced with permission from the publisher. ABSTRACT AimThe over-arching aim of this thesis was to study some metabolic functions of the gut microflora in children with known or screening detected celiac disease (CD) and their first-degree relatives. Materials Study I. A number of 36 untreated CD children, 47 after at least 3 months on glutenfree diet (GFD) and 42 healthy controls (HC). Study II. A number of 76 first-degree relatives to CD children and 93 healthy controls (HC). Study III. A number of 17 screening detected CD children were included to be compared with the untreated children and controls from study I; with exchange of one child in the untreated group, due to low age. Study IV. A comparative study regarding correlation between iso-forms of short chain fatty acids (SCFAs) in humans as well as in animals. Methods Faecal short chain fatty acids were measured in all four studies. Additionally faecal tryptic activity (FTA) was measured in study II. Major findingsAll groups of CD children demonstrated a similar SCFAs profile, i.e. significantly more total SCFAs and acetic acid and a strong tendency to more iso-butyric and iso-valeric acids compared with HC. The first-degree relatives demonstrated another SCFAs profile, i.e. significantly less total SCFAs and acetic acid and significantly more FTA than HC. Conclusions and future outlookBased upon the strong similarities between all groups of CD children we are allowing ourselves hypothesising that CD children have a "celiacogenic" flora compared with healthy controls. In a similar way it can be said that the first-degree relatives are harbouring a "celiacprotective" microflora. Our findings open up for challenging new diagnostic, therapeutic and prognostic possibilities.