Small Intestinal Bacterial Overgrowth

Excerpt

Small intestinal bacterial overgrowth (SIBO) is the presence of excess colonic bacteria in the small intestine. These excess organisms result in multiple intestinal symptoms like abdominal pain, bloating, diarrhea, and rarely malabsorption. . The proximal small intestine typically contains relatively few bacteria due to the presence of stomach acid and the effects of peristalsis. Lactobacilli, enterococci, facultative anaerobes, and gram-positive anaerobes are predominantly organisms in the small intestine. The concentration of organisms rarely exceeds ten organisms/mL in the jejunum. Bacteroids, Lactobacillus, Clostridium, and bifidobacteria, the predominant organisms in the colon, are seldom seen in the proximal small intestine. The terminal ileum microbiome is intermediate between the proximal small intestine (aerobic flora) and colon (densely anaerobic); in the absence of an ileocecal valve terminal ileum, the microbiome is similar to the colon with ten organisms/ml. When the protective mechanisms (peristalsis, stomach acid) against excessive bacterial growth fail, small intestinal bacterial overgrowth (SIBO) can manifest. Due to recent advances in medicine and increased awareness and understanding, SIBO is considered by most clinicians as a differential diagnosis in patients with non-specific gastrointestinal complaints.