Small intestine, microbiota

Zoetendal EG, Raes J, van den Bogert B, et al. The human small intestinal microbiota is driven by rapid uptake and conversion of simple carbohydrates. ISME ]. 2012 6 1415-1426. 

The chicken intestinal microbiota is composed principally of Gram-positive bacteria (Gong et al., 2002). The lactobacilli are predominant in the small intestine (with smaller numbers of streptococci and enterobacteria), whereas the caecal flora is composed mainly of anaerobes and fewer numbers of facultative bacteria. Predominant cultured flora of the ileum of chicken include Lactobacillus, Streptococcus, E. coli and Eubacterium, while Eubacterium and Bacteroides dominated the caecum flora. 

Recent molecular studies have confirmed earlier culture-based work that describes the microbiota of the small intestine as comprising between 10 and 10 microorganisms per mL ileal fluid. Samples of ileal fluid collected from ileostomy patients analyzed using the HITCHIP gut microbiota 16S rRNA targeted microarray revealed a microbiota dominated by lactobacilli, streptococci, clostridia with a lower abundance of strict anaerobes including... 

Anthocyanins seem to be absorbed in the upper G1 (stomach and small intestine) mainly in the parent forms. In addition, they, themselves and/or their metabolites seem to be absorbed after a microbial action, and microbiota seems to constitute the main responsible factor for anthocyanin bioavailability. 

The recent development of next-genCTation sequencing techniques has offered a deeper and more comprehensive view on the composition of the human microbiota and has also chaUenged some pre-conceived ideas about LAB residing in the human intestine. Both culturing techniques and molecular approaches indicated that lactobacUU account for a small percentage of the ovCTaU human intestinal microbiota (Walter 2008). However, it remains unclear whether these LAB are permanent... 

Although L. lactis represents a promising candidate for a live mucosal vector delivery system, some laboratories have further explored the capacity of other bacteria with better intrinsic propaties such as lactobacilli. Specific strains of lactobacilli have been characterized to possess probiotic properties (microorganisms that provide health benefits when consumed). Furthermore, some lactobaciUi species such as Lact. casei, Lact. acidophilus, Lact. gasseri, Lact. plantarum, and Lact. fermentum are able to persist for longer periods than L lactis in the GIT. Additionally, some species of lactobacilli are part of the microbiota that colonized the mammalian small intestine. The interaction of lactobacilli with the intestinal mucosa is an important factor because this enhances mucosal immune responses. Since the end of the 1990s, researchers have been exploiting these inherent properties of lactobacilli to make them an attractive alternative and safer delivery system for molecules and compounds with health benefit (Rush et al. 1995 Pouwels et al. 1996). 

Animals, plants, and fungi are incapable of producing cobalamin it is the only vitamin that is exclusively produced hy microorganisms, particularly by anaerobes (Roth et al. 1996 Martens et al. 2002 Smith et al. 2007). Furthermore, biochemical and genomic data indicate that only a few bacteria and archaea possess the abOity to produce this vitamin (Roth et al. 1996 Rodionov et al. 2003). Adult ruminant animals and strict vegetarians can obtain the vitamin in specialized bacteria present in the rumen. Humans do not have such microbiota in their small intestine and must absorb the co-enzyme from natural sources such as animal meats (especially liver and kidney), fish, eggs, and pharmaceutical products (Herbert 1996). 

The final criterion for a prebiotic is that its fermentation in the colon has some beneficial impact on host health. In vitro studies using models of the colonic microbiota inoculated with human feces and studies in animals, have shown that fermentation of prebiotic fructans leads to accumulation of acetate and butyrate in intestinal/gut model contents. Fermentation of other prebiotics and certain dietary fibers has also been shown to increase propionate production in these systems. Small amounts of lactate and succinate can also be observed using in vitro models, but in vivo, these SCFA are rapidly converted into butyrate and propionate by the gut microbiota. Bifidobacteria and lactobacilli ferment carbohydrates mainly to acetate and lactate, but do not themselves produce butyrate. Recent studies have shown that dominant members of the Firmicutes, Eubacterium halli, Roseburia, Faecalibacterium prausnitzii and Anaerostipes caccae are able to cross-feed off acetate and lactate within the colonic milieu converting them into butyrate, providing a mechanism by which prebiotic modulation of acetate-produdng bifidobacteria can lead to elevated butyrate concentrations within the SCFA have been implicated... 

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