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The human distal small intestine (ileum) has a distinct microbiota
In contrast to the relative stability of the Gut microbiota, the biomass of the human small gut microbiota and its substrain composition can be highly dynamic
Sequential sampling of the ileum before and after stoma surgery revealed that the microbiota of the ileostomy resembled that of the entire small intestine.
It has been confirmed that ileal and colonic stoma microbiota are distinct, and two types of instability in ileal host-microbial relationships have been observed: inter-digestive flushing followed by the rapid postprandial bloom of bacterial biomass, and the appearance and disappearance of subphyla within individual taxa then feeding
Members belonging to Lactobacillales or Proteobacteria are the major residents of the small intestine
The small intestine contains a very different abundance and composition of bacteria, with much more dynamic variation than the large intestine
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The microbiota of the small intestine is characterized by its rapid import, conversion of relatively small carbohydrates, and rapid adaptation to general nutrient availability
The small intestine is more acidic and has higher levels of oxygen and antimicrobials than the colon
The small intestine microbial community is dominated by fast-growing facultative anaerobes that tolerate the combined effects of bile acids and antimicrobials while competing for simple carbohydrates available in this region of the gastrointestinal tract.
Proteobacteria and Lactobacillales / Lactic acid bacteria (LAB) are the major residents of the small intestine
The small intestine is rich in mono- and di-saccharides as well as amino acids, which support the growth of Proteobacteria and Lactobacillales
Because in the small intestine, the mucus layer is thinner and more penetrable by bacteria or potential toxins, enterocytes, Paneth cells, and immune cells secrete antimicrobial proteins for host defense
Due to its proximity to the stomach, the small intestine contains high concentrations of acids, oxygen, and antimicrobials, thereby restricting bacterial growth to predominantly fast-growing anaerobes that can adhere to epithelia or mucus
The microbiota of the small intestine is characterized by its rapid import, conversion of relatively small carbohydrates (mono- and di-saccharides), and rapid adaptation to general nutrient availability
Mono- and di-saccharides as well as amino acids support the growth of Proteobacteria and Lactobacillales
Except for the absence of villi, the more numerous goblet cells, the architecture of the colon closely resembles that of the small intestine (duodenum + jejunum + ileum)
The small intestine contains a very different abundance and composition of bacteria, with much more dynamic variation than the large intestine
The small intestine is more penetrable by bacteria or potential toxins. Nevertheless, enterocytes, Paneth cells, and immune cells secrete antimicrobial proteins for host defense
In contrast to the stomach and the colon, there is only one mucus layer in the small intestine
The small intestine has fewer bacteria than the colon because the body uses several methods to keep them in check. These methods include quick movement of food, antimicrobial substances, enzymes, and bile
If these methods fail, too many bacteria can grow in the small intestine, leading to problems with absorbing nutrients because the bacteria use up the nutrients.