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Small-bowel bacterial overgrowth 

Small-bowel bacterial overgrowth

Small-bowel bacterial overgrowth

Richard A. Schatz

and Phillip P. Toskes



Pathogenesis – discussion of the possible role of proton pump inhibitors

Diagnosis – comparison of lactulose hydrogen, glucose hydrogen and 14C D-Xylose breath tests; preliminary studies of circulating CdtB antibodies as a diagnostic tool.

Updated on 30 Jul 2015. The previous version of this content can be found here.
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date: 23 April 2017

Malabsorption in a patient with overgrowth of bacteria in the small intestine is known as small-bowel bacterial overgrowth (SBBO). Predisposing causes include sustained hypochlorhydria induced by proton pump inhibitors, small-intestinal stagnation due to anatomical (e.g. diverticulosis, postsurgical) or motor (e.g. scleroderma) abnormalities, and chronic pancreatitis.

Presenting symptoms include diarrhoea, steatorrhoea, weight loss, and flatulence. Investigation may reveal low levels of cobalamin (metabolized by Gram-negative anaerobes), increased serum folate (synthesized by overgrowth flora), and decreased urinary excretion of xylose (intraluminal degradation of the sugar by overgrowth flora).

Definitive diagnosis is time-consuming and expensive, requiring a properly collected and appropriately cultured aspirate from the proximal small intestine revealing a total concentration of bacteria generally greater than 105 organisms/ml, with Bacteroides, anaerobic lactobacilli, coliforms, and enterococci all likely to be present. Alternative investigations are frequently employed, of which the most reliable is the 14C-xylose breath test, with elevated levels of 14CO2 found in the breath after 30 min in SBBO.

Aside from supportive care, specific treatment is with an antimicrobial that is effective against both aerobic and anaerobic enteric bacteria, e.g. tetracycline (but resistance is an increasing problem), amoxicillin-clavulanic acid, or norfloxacin.

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