If the small intestine is massively overgrown with bacteria or colonised by actually harmless colon bacteria (bacterial overgrowth), this leads to a serious disturbance of the homeostasis in the bacterial ecosystem (dysbiosis) with serious digestive disorders.
The clinical appearance depends crucially on the underlying disease. Typical symptoms of bacterial overgrowth of the small intestine include excessive gas formation with flatulence (meteorism), flatulence, abdominal tightness, diarrhoea and abdominal pain.
Unrecognised or untreated bacterial overgrowth in the small intestine usually results in chronic malassimilation syndrome with weight loss. Corresponding symptoms up to full-blown osteomalacia, coagulation disorders and night blindness can result from the consecutive deficiency of vitamins D, K, A and B12.
Simple functional tests such as the H2 breath test with a defined test drink of 50- 100 g glucose are uncomplicated to perform, but have a lower specificity. The test is based on measuring the concentration of hydrogen (H2) in the exhaled air before and after a test drink. Hydrogen is produced in every person only by bacterial decomposition of sugars and other carbohydrates. Provided there is no defective colonisation of the small intestine, such bacterial fermentation takes place almost exclusively in the large intestine. The resulting hydrogen is excreted rectally in the form of flatus, but is also absorbed into the blood and exhaled through the lungs. The amount of hydrogen in the exhaled air can be measured with special analysers (usually a gas chromatograph). The proportion of gas exhaled via the lungs rises measurably above a critical limit (usually 20 ppm) in the case of bacterial overgrowth in the small intestine.
Conservative therapy is primarily based on the use of antibiotics . Unfortunately, controlled studies on this topic are almost non-existent. Antibiotic treatment is initially very effective in most cases. The response to therapy is shown by a decrease in diarrhoea and abdominal complaints as well as an improved absorption of fat and vitamin B12 within one week after the start of therapy. Most patients remain symptom-free for several months after taking rifaximin antibiotics for 7-14 days.
Rifaximin with its pyridoimidazole structure and neomycin or paromomycin as non-absorbable aminoglycosides are practically not absorbed from the intestine.
Another therapeutic approach is the prescription of probiotics, possibly also in combination with antibiotics. Unfortunately, there are no systematic studies on this. The data are most in favour of the use of preparations containing different strains of lactobacilli. Observational clinical studies show that antibiotics are more effective than probiotics in the initial treatment. Another option is to treat patients first with a short course of antibiotics and then with probiotics in the longer term.