Part of the series Clinical Gastroenterology pp 189-207


Bacterial Overgrowth

  • Rosemary J. YoungAffiliated withBoys Town National Research Hospital
  • , Jon A. VanderhoofAffiliated withChildren’s HospitalHarvard Medical School

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The human gastrointestinal tract typically contains 300–500 bacterial species. Most bacterial species are acquired during the birth process and although some changes to the flora may occur during later stages of life, the composition of the intestinal microflora remains relatively constant. Small bowel bacterial overgrowth (SBBO) is defined as an excessive increase in the number of bacteria in the upper gastrointestinal tract leading to the development of symptoms. Etiologic factors in the development of SBBO include anatomic abnormalities, functional abnormalities including altered intestinal motility, and multifactorial issues such as malnutrition of the host and abnormalities of the immune system. Symptoms of SBBO include abdominal cramping, bloating, diarrhea, dyspepsia, and/or weight loss. Systemic distribution of bacterial antigen–antibody complexes may cause rashes, arthritis, and nephritis. Colitis or ileitis may also occur due to SBBO. Although diagnosis of bacterial overgrowth is classically based upon demonstration of an increase of bacterial content by aspiration and culture of upper intestinal fluids, these methods have several limitations. For this reason, a variety of non-invasive diagnostic tests have been devised for the diagnosis of SBBO. A hydrogen breath test is the most common method used. Alternative tests include the measurement of the byproducts of luminal bacteria metabolism in urine or blood and small bowel biopsies demonstrating often inflammatory changes. Treatment of SBBO commonly involves rotating broad-spectrum oral antibiotics. When significant intestinal inflammation is present, anti-inflammatory therapy with sulfasalazine or corticosteroids may be used. Regular toileting and colonic flushing with may also be used. Surgical corrections of anatomic abnormalities, such as stricture, fistula, diverticuli, are often helpful. Segments of dilated, poorly peristaltic bowel may be corrected with lengthening operations. Probiotic therapy in SBBO may be effective in reducing the use of antibiotic therapy and controlling symptoms; however, conclusive studies are needed. Nutritional support is an essential part of the management of SBBO both as a therapeutic measure and in the prevention of malnutrition.

Key Words

Small bowel bacterial overgrowth SIBO Microflora Chronic diarrhea Breath test