Show Summary Details
Page of

Bacterial overgrowth of the small intestine 

Bacterial overgrowth of the small intestine
Bacterial overgrowth of the small intestine

Stephen J. Middleton

, and Raymond J. Playford

Page of

PRINTED FROM OXFORD MEDICINE ONLINE ( © Oxford University Press, 2021. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy and Legal Notice).

date: 05 March 2021

Small intestinal bacterial overgrowth can be defined as the presence of excessive bacteria in the small intestine which can interfere with digestion and absorption. Predisposing causes include sustained hypochlorhydria induced by proton pump inhibitors, small intestinal dysmotility and stasis due to anatomical or motor abnormalities, and reduced antibacterial activity as seen in immunological deficiency and chronic pancreatitis. Presentation is predominantly from consequences of malabsorption, including gastrointestinal symptoms (e.g. diarrhoea or steatorrhoea) and features of specific nutrient malabsorption (e.g. osteoporosis, anaemia, neuropathy, and night blindness). Definitive diagnosis is difficult, requiring a properly collected and appropriately cultured aspirate from the proximal small intestine revealing a total concentration of a mixed growth of bacteria generally greater than 105 organisms/ml. Alternative investigations frequently used include glucose/lactulose breath tests or either the 13C- or 14C-xylose breath test, with elevated levels of 13CO2 or 14CO2 found in the breath. There may be low levels of cobalamin (metabolized by Gram-negative anaerobes), increased serum folate (synthesized by overgrowth flora), and increased urinary indicans (intraluminal product of bacterial tryptophan metabolism). Aside from treatment of any nutritional deficiencies, specific treatment is with an antimicrobial that is effective against both aerobic and anaerobic enteric bacteria (e.g. doxycycline, amoxicillin–clavulanic acid, rifaximin, or ciprofloxacin), which can be administered in rotation to reduce antibiotic resistance. Where possible and appropriate, correction of any underlying cause should also be performed.

Access to the complete content on Oxford Medicine Online requires a subscription or purchase. Public users are able to search the site and view the abstracts for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can't find the answer there, please contact us.