The concept of small intestinal bacterial overgrowth in relation to functional gastrointestinal disorders

doi:10.1016/j.nut.2010.01.005

Nutrition

Volume 26, Issues 11–12, November–December 2010, Pages 1038-1043

https://doi.org/10.1016/j.nut.2010.01.005 Get rights and content

Abstract

The role of small intestinal bacterial overgrowth in the genesis of functional gut symptoms is controversial, but therapeutic benefits of antibiotics in controlled trials have highlighted the need to better evaluate and manage this state. Its definition is unclear due to limitations in assessing the microbiota in the small intestine and uncertainty regarding what is normal. Methodologies to detect bacterial overgrowth in clinical practice have limitations. The most commonly used is breath hydrogen testing after lactulose, but this cannot readily differentiate rapid orocecal transit from small intestinal bacterial overgrowth. Symptom generation might derive from fermentation of dietary carbohydrates with resultant luminal distension, from impairment of digestion and absorption with changes to the luminal composition, or by interaction with the enteric nervous system and immune system with subsequent changes in nociceptive thresholds and/or motility patterns. Therapy is usually directed toward reducing the bacterial load with antibiotics, but altering the functional properties of the microbiota by reducing or changing the supply of fermentative substrate or by the use of probiotics are promising alternatives. Controversy will continue until concepts are broadened, consensus in definition is reached, and evaluation of efficacy of candidate therapies is more rigorous.

Section snippets

Small intestinal bacterial overgrowth—a flawed concept?

The concentration of bacteria in the jejunum and ileum is usually quoted as 10⁴–10⁸ colony-forming units (CFU)/mL, which contrasts to 10⁹–10¹² CFU/mL in the large bowel. SIBO has been traditionally defined according to the number and often type of culturable bacteria in duodenal or jejunal aspirates; for example, 10⁵ CFU/mL of “colonic-type” bacteria has been commonly used [1], [2], [3], [4], [5]. Such a definition, however, presents four important conceptual difficulties.

First, because much of

How to detect SIBO

Multiple techniques have been used to detect SIBO and have recently been systematically reviewed [10]. The accurate detection in clinical practice of SIBO has been difficult and no test can be considered truly validated due to the lack of a gold standard. Culture-based techniques have convincingly demonstrated excessive density of bacteria in the proximal small intestine in association with motility disturbances or anatomical abnormalities in which stasis is the common denominator [12].

SIBO—normal or abnormal?

One of the conceptual stumbling blocks around SIBO has been the consideration by most authors that SIBO is abnormal. There would be little argument that a positive glucose breath test in a patient with anatomical abnormalities of the proximal small intestine indicates the presence of an abnormal population of bacteria. However, the same might not apply to a patient with normal anatomy and functional gut symptoms. Likewise, a test that is positive for SIBO in a moderate proportion of healthy

Mechanisms by which SIBO may be associated with functional gut symptoms

While the association of SIBO with functional gut symptoms remains controversial, there is evidence that SIBO potentially may be involved in triggering symptoms. This might occur via two mechanisms. The first is by the impairment of digestion and/or absorption. SIBO may lead to deconjugation of bile salts with subsequent fat malabsorption, leading to fatty acid diarrhea [24]. It has also been demonstrated by breath hydrogen studies that malabsorption of fructose and possibly lactose is

Therapeutic approaches to SIBO

In light of the potential mechanisms by which SIBO might cause symptoms, therapeutic approaches theoretically include reducing the bacterial load and/or changing the functional properties of the microbiota.

Conclusions

Managing functional gut symptoms continues to be a clinical challenge, and better targeting of therapy toward factors that are pathogenically related to the genesis of symptoms is needed. The concept of SIBO has provided an exciting new potential therapeutic target. The presence of SIBO is probably best assessed by examining the time of first rise in breath hydrogen after lactulose, but the finding of ERBHAL is not specific for, only suggestive of, SIBO. ERBHAL itself is a normal phenomenon,

Acknowledgments

JSB was in receipt of a Sir Robert Menzies Memorial Research Scholarship in the Allied Health Sciences and received a Postdoctoral Publication Award from Monash University.

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: Both authors contributed equally to the text.

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ReviewThe concept of small intestinal bacterial overgrowth in relation to functional gastrointestinal disorders

Abstract

Section snippets

Small intestinal bacterial overgrowth—a flawed concept?

How to detect SIBO

SIBO—normal or abnormal?

Mechanisms by which SIBO may be associated with functional gut symptoms

Therapeutic approaches to SIBO

Conclusions

Acknowledgments

Am J Gastroenterol

Gastroenterology

Gastroenterology

Am J Gastroenterol

Am J Med Sci

Am J Gastroenterol

Eur J Cancer

J Americ Diet Ass

Clin Gastroenterol Hepatol

The pathogenesis of gastrointestinal bacterial overgrowth

Chemotherapy

Enteric bacterial flora and bacterial overgrowth syndrome

Semin Gastrointest Dis

Small bowel bacterial overgrowth syndrome

Dig Dis

Small bowel bacterial overgrowth: presentation, diagnosis, and treatment

Curr Treat Options Gastroenterol

The normal intestinal microbiota

Curr Opin Infect Dis

Benefits of breath hydrogen testing following lactulose administration in analyzing carbohydrate malabsorption

Eur J Gastroenterol Hepatol

Alternative pathways for hydrogen disposal during fermentation in the human colon

Gut

Methane, a gas produced by enteric bacteria, slows intestinal transit and augments small intestinal contractile activity

Am J Physiol

Small intestinal bacterial overgrowth

Scand J Gastroenterol

A systematic review of diagnostic tests for small intestinal bacterial overgrowth

Dig Dis Sci

Bacteriological method for detecting small intestinal hypomotility

Am J Gastroenterol

Review
The concept of small intestinal bacterial overgrowth in relation to functional gastrointestinal disorders