Center for Digestive Diseases

UNM Hospitals Center
for Digestive Diseases

1001 Martin Luther King Ave. NE
Albuquerque, New Mexico 87106

(505)272-2530 or

UNMH: (505)272-6839
CDD: (505)925-7849

Small Intestinal Bacterial Overgrowth

What is small intestinal bacterial overgrowth?

Bacteria in our GI tract play a critical role in many processes required for good health.  Although a predominance of these bacteria are found in the large bowel, there is a sizable concentration of bacteria also found in the small bowel.   In some conditions, the concentration of bacteria in the small bowel may increase to levels above those normally expected.   Furthermore, this may accompany an alteration in the ratio of the various bacterial phyla, family, species, etc. that is normally found in the small bowel.  This change in the number and make-up of the small bowel bacteria has been termed small intestinal bacterial overgrowth.

What are the symptoms of small intestinal bacterial overgrowth?

There can be numerous symptoms potentially attributable to small intestinal bacterial overgrowth.  Some of the most common symptoms include abdominal pain, distention, and excessive gas production.  In some people, small intestinal bacterial overgrowth may result in chronic diarrhea.  Alternatively in some people, it is thought small intestinal bacterial overgrowth may result in constipation.

What causes small intestinal bacterial overgrowth?

Small intestinal bacterial overgrowth may develop in the setting of certain anatomic abnormalities, such as a small bowel diverticulum or after surgery during which a “blind limb” is created or during which the ileocecal valve is removed.   Also conditions in which normal motility in the small bowel is disrupted, whether it is due to an abnormality in the nerves or the muscles, may allow small intestinal bacterial overgrowth to develop.

How is small intestinal bacterial overgrowth diagnosed?

There is not a perfect test to definitively diagnose small intestinal bacterial overgrowth.  Some centers choose to perform an endoscopy procedure during which a bacterial sample from the deep small bowel is obtained, and quantification of the number of bacteria grown in cell culture is attempted.  This approach is semi-invasive and inherently involves some inaccuracies.  An alternative way to try to establish the diagnosis is a lactulose breath test.  This is a noninvasive test that can be easily obtained in an office setting.  After drinking a glass of lactulose, a syrupy carbohydrate solution, the patient’s exhaled breath is collected and analyzed over a period of two to three hours. Graphing the amount and type of exhaled gas gives a pattern that supports or refutes the diagnosis of small intestinal overgrowth.     

What is the treatment for small intestinal bacterial overgrowth?

Treatment of small intestinal bacterial overgrowth is directed at trying to decrease the concentration of bacteria back to more “normal” levels and thus alleviate symptoms.  A treatment course often lasts 10 days and includes an antibiotic which specifically targets the types of bacteria found in the intestine.  If there is an inadequate response to the initial antibiotic treatment, the patient may be retreated with an alternative regimen.