Small intestinal bacterial overgrowth

Bacterial overgrowth of the small intestine (SIBO) is defined as the presence of excessive numbers of bacteria causing gastrointestinal symptoms such as bloating, nausea, abdominal pain, diarrhea and malabsorption. Diagnosis is made through cultural detection of bacteria from small intestinal aspirates or indirectly through breath tests, which can detect the bacterial fermentation products hydrogen (H 2 ) and methane (CH 4 ) in exhaled air after carbohydrate provocation. SIBO can be caused by various mechanisms such as reduced intestinal motility, altered gastrointestinal anatomy, reduced gastric acid or pancreatic enzyme production, altered bile acid metabolism, or immune defects. Accordingly, SIBO often develops secondary to different underlying diseases such as blind loop syndromes, gastrointestinal motility disorders including scleroderma and several neurological diseases, several chronic diseases of the gut, liver and pancreas including irritable bowel syndrome and others. Symptoms are triggered by direct bacteria-induced damage of the intestinal barrier or by bacterial metabolism such as the fermentation of dietary carbohydrates with increased gas production. The therapy includes the treatment of the underlying disease to eliminate the causal factors as much as possible, compensation for micro- and macronutrient deficiencies and treatment with antibiotics. Moreover, probiotics and dietetic therapy such as a low FODMAP diet should be considered. Recurrences are common and may necessitate repeated therapy. This review summarizes the current knowledge on SIBO pathophysiology, prevalence, diagnosis, and treatment.