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Excessive bacterial growth in the small intestine
Last reviewed: 05.07.2025
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Small intestinal bacterial overgrowth may be due to anatomical changes in the intestine or gastrointestinal motility disorders, as well as gastric secretion insufficiency. These disorders may lead to vitamin deficiencies, fat malabsorption, and malnutrition. Diagnosis is made by a 14 -Xylose breath test. Treatment for small intestinal bacterial overgrowth consists of oral antibiotics.
[ What causes small intestinal bacterial overgrowth?
The normal proximal small bowel contains less than 10 bacteria/mL, mostly gram-positive aerobic bacteria. This low bacterial count is maintained by normal peristalsis, adequate gastric acid secretion, mucus, secretory IgA, and a functioning ileocecal sphincter.
Typically, bacterial overgrowth occurs when anatomical changes cause stasis of intestinal contents. These changes include small-bowel diverticulosis, blind intestinal loops after surgery, postgastrectomy status (especially in the afferent loop after Billroth II surgery), stenosis, or partial obstruction. Dysmotility disorders associated with diabetic neuropathy, systemic sclerosis, amyloidosis, and idiopathic intestinal pseudo-obstruction may also promote bacterial overgrowth. Achlorhydria and idiopathic intestinal motility changes may cause bacterial overgrowth in the elderly.
Excess bacteria consume nutrients, including vitaminB12 and carbohydrates, leading to energy deficiency and vitamin B12 deficiency . However, because bacteria synthesize folate, folate deficiency is rare. Bacteria deconjugate bile salts, causing failure of micelle formation and subsequent fat malabsorption. Bacterial overgrowth in severe cases damages the intestinal mucosa.
Symptoms of Small Intestinal Bacterial Overgrowth
In many patients, small intestinal bacterial overgrowth is asymptomatic and presents only with weight loss or malnutrition. Sometimes, severe diarrhea or steatorrhea may occur.
Diagnosis of small intestinal bacterial overgrowth
Some clinicians consider the efficacy of empirical antibiotic therapy as a diagnostic test. However, because bacterial overgrowth may resemble other malabsorption disorders (eg, Crohn's disease) and because the side effects of antibiotic therapy may worsen the disease, the cause should be clearly established.violations.
The standard for establishing the diagnosis is quantitative determination of the microflora in the intestinal contents obtained by aspiration (bacteria count > 10 /ml). This method, however, requires endoscopy. Breath tests are noninvasive and easy to perform. The 14- Xylose breath test is the most sensitive and specific. In addition, it is necessary to perform an examination of the upper gastrointestinal tract, including the small intestine, in order to identify predisposing anatomical abnormalities.
Treatment of small intestinal bacterial overgrowth
Treatment of small intestinal bacterial overgrowth consists of oral antibiotics for 10 to 14 days. Empirical regimens include tetracycline 250 mg 4 times daily, amoxicillin/clavulanic acid 250 to 500 mg 3 times daily, cephalexin 250 mg 4 times daily, trimethoprim-sulfamethoxazole 160/800 mg 2 times daily, and metronidazole 250 to 500 mg 3 or 4 times daily. Antibiotics should be based on culture and sensitivity results. Underlying conditions and nutritional deficiencies (eg, vitamin B 12 ) should be addressed.