Small Intestinal Bacterial Overgrowth
Soon after birth, the previously sterile infant gastrointestinal tract becomes colonized by microbes. Because of the bactericidal action of gastric acid and the sweeping of the intestinal lumen by peristalsis, the proximal small intestine is normally colonized by a relatively small number of bacteria, consisting mainly of Gram-positive microbes and anaerobes from the oral cavity. In the ileum, an increase in microbial colonization of up to 109 colony-forming units (CFU)/mL occurs, due mainly to Gram-negative microbes and anaerobes. Finally, the colon contains an abundance of mostly anaerobic microbes at a concentration of up to 1012 CFU/mL.
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