IBS-D is associated with elevated hydrogen numbers on breath tests while IBS-C is associated with elevated methane numbers on breath tests. Subsequent studies demonstrated statistically significant reduction in IBS symptoms following therapy for SIBO.Various mechanisms are involved in the development of diarrhea and IBS-D in bacterial overgrowth. First, the excessive bacterial concentrations can cause direct inflammation of the small bowel cells, leading to an inflammatory diarrhea. The malabsorption of lipids, proteins and carbohydrates may cause poorly digestible products to enter into the colon. This can cause diarrhea by the osmotic drive of these molecules, but can also stimulate the secretory mechanisms of colonic cells, leading to a secretory diarrhea.There is a lack of consensus however, regarding the suggested link between IBS and SIBO. Other authors concluded that the abnormal breath results so common in IBS patients do not suggest SIBO, and state that "abnormal fermentation timing and dynamics of the breath test findings support a role for abnormal intestinal bacterial distribution in IBS." There is general consensus that breath tests are abnormal in IBS; however, the disagreement lies in whether this is representative of SIBO. Etiology and risk factors
Certain people are more predisposed to the development of bacterial overgrowth because of certain risk factors.
It compares well to jejunal aspirates in making the diagnosis of bacterial overgrowth. Carbon-13 (13C) and carbon-14 (14C) based tests have also been developed based on the bacterial metabolism of D-xylose. Increased bacterial concentrations are also involved in the deconjugation of bile acids. The glycocholic acid breath test involves the administration of the bile acid 14C glycocholic acid, and the detection of 14CO2, which would be elevated in bacterial overgrowth.However, some physicians suggest that if the suspicion of bacterial overgrowth is high enough, the best diagnostic test is a trial of treatment. If the symptoms improve, an empiric diagnosis of bacterial overgrowth can be made.There is insufficient evidence to support the use of inflammatory markers, such as fecal calprotectin, to detect SIBO. Treatment
Treatment strategies should focus on identifying and correcting the root causes, where possible, resolving nutritional deficiencies, and administering antibiotics. This is especially important for patients with indigestion and malabsorption. Although whether antibiotics should be a first line treatment is a matter of debate. Some experts recommend probiotics as first line therapy with antibiotics being reserved as a second line treatment for more severe cases of SIBO. Prokinetic drugs are other options but research in humans is limited. A variety of antibiotics, including tetracycline, amoxicillin-clavulanate, metronidazole, neomycin, cephalexin and trimethoprim-sulfamethoxazole have been used; however, the best evidence is for the use of rifaximin, a poorly-absorbed antibiotic.