The test uses the principle that the metabolism of either lactulose or glucose as its carbohydrate substrate by bacteria will produce either hydrogen or methane. A carbohydrate breath test is a noninvasive, fast, and inexpensive test. When a patient presents with signs and symptoms concerning SIBO, the diagnosis garners further support with a positive carbohydrate breath test or a bacterial concentration of more than 1000 colony-forming units/mL in a jejunal aspirate culture. There is no validated gold standard diagnostic test for small intestinal bacterial overgrowth.
Unless severe malnutrition is evident, physical examination in these patients is generally nonrevealing. SIBO has been implicated in the development of nonalcoholic fatty liver disease and hepatic encephalopathy. Patients with SIBO associated with short bowel syndrome or a jejunoileal bypass can develop this syndrome. This syndrome results from bacterial fermentation of unabsorbed carbohydrates. ĭ-lactic acidosis, a rare neurological syndrome, is characterized by altered mental status, slurred speech, seizures, and ataxia. In contrast, bacterial synthesis results in the elevation of folate and vitamin K levels. Vitamin B1 and B3 deficiencies occur due to bacterial overutilization. Vitamin B12 deficiency occurs from ileal mucosal damage to cobalamin binding sites. Steatorrhea and weight loss from fat malabsorption may manifest as well. The clinical manifestations of small intestinal bacterial overgrowth classically include a combination of abdominal discomfort with bloating, flatulence, or chronic watery diarrhea. Immunodeficiency disorders, such as acquired immune deficiency syndrome, combined variable immunodeficiency, and IgA deficiency, are associated with an increased risk of SIBO. Lastly, immunoglobin A, which is abundant in the gastrointestinal tract, also prevents bacterial proliferation and maintains intestinal immunity. Such anatomic disorders may include small intestinal diverticulosis, bowel strictures, post-operative adhesions, gastric bypasses with blind intestinal loops, and ileocecal resection. Anatomic abnormalities lead to stasis of the bowels, which may predispose them to SIBO.
Īn intact ileocecal valve and antegrade motility prevent retrograde translocation of colonic bacteria. SIBO is associated with disorders of abnormal gastrointestinal motility, such as irritable bowel syndrome, narcotic use, post-radiation enteropathy, hypothyroidism, diabetes mellitus, and scleroderma. Migrating motor complexes are responsible for peristalsis and cleansing the small intestine. Chronic pancreatic insufficiency is associated with SIBO. Also, proteolytic enzymes digest and degrade bacteria in the intestines. Conditions that cause achlorhydria are associated with SIBO. Upon ingestion of food, gastric acids and bile destroy and prevent bacteria from passing through the intestines. When these protective barriers fail, SIBO occurs. There are many important host defense mechanisms against bacterial overgrowth. The etiology of small intestinal bacterial overgrowth is complex. Due to recent advances in medicine and increased awareness and understanding, SIBO is now often considered in most clinicians’ differential diagnoses in patients with non-specific gastrointestinal complaints. When the protective mechanisms against excessive bacterial growth fail, small intestinal bacterial overgrowth (SIBO) can manifest. Bacteroids are predominant organisms in the colon, and concentrations can reach 10organisms per mL. The concentration of organisms rarely exceeds 10/mL in the small intestine. Lactobacilli, enterococci, facultative anaerobes, and gram-positive anaerobes are predominantly organisms in the small intestine. The proximal small intestine normally contains relatively very few bacteria due to the presence of stomach acid and the effects of peristalsis. The presence of these excess organisms, resulting in multiple intestinal symptoms, is mandatory.
Small intestinal bacterial overgrowth (SIBO) is defined as the presence of excess colonic bacteria in the small intestine.