Small Intestinal Bacterial Overgrowth

In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan.


Small intestinal bacterial overgrowth (SIBO) is defined as the presence of excess colonic bacteria in the small intestine. The presence of these excess organisms, resulting in multiple intestinal symptoms, is mandatory. However, malabsorption rarely occurs.The proximal small intestine normally contains relatively very 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 10/mL in the small intestine. Bacteroids are predominant organisms in the colon, and concentrations can reach 10organisms per mL.

When the protective mechanisms 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 now often considered in most clinicians’ differential diagnoses in patients with non-specific gastrointestinal complaints.

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