Normal gut ﬂora may provide several beneﬁcial effects to the host.
These include fermentation of un-digested dietary residue and endogenous mucus producing short chain fatty acids, which are nutrients to the colonic epithelial cells and conservation of energy, absorption of NaCl and water, particularly from the right colon, synthesis of vitamin K, control of epithelial cell proliferation, protection against pathogens by a barrier effect and training of the immune system. The small intestine of germ free mice has thin and irregular villi, reduced crypt size, increased number of Peyer’s patches, and inﬁltration of leukocytes in lamina propria. Alteration in the normal ﬂora leads to disturbance in the intestinal homeostasis.
Immune activation in response to SIBO recruits increased number of intraepithelial lymphocytes, mast cells and enterochromaﬃn cells. Mediators of host immune response trigger the enteric nervous system altering GI motility and visceral hypersensitivity, which are the major pathophysiological mechanisms of IBS.
Overgrowth of sulfate reducing bacteria may play an important role in patients with IBS. An association was found between bacterial derived hydrogen sulﬁde (H 2 S) and visceral hypersensitivity. H 2 S is known to act as gaseous neurotransmitters inducing the contraction of detrusor muscle in the urinary bladder. Recently, a study has shown that H 2 S produced by sulphate reducing bacteria may play role in pathogenesis of SIBO. Fibromyalgia, a condition associated with IBS, is also associated with SIBO. A study showed that all 42 patients with ﬁbromyalgia had positive breath test. This percentage was signiﬁcantly higher than the control population. These data might suggest that somatic hypersensitivity is also inﬂuenced by altered gut ﬂora.
did you know?
E. coli is commonly isolated in patients with bacterial overgrowth Certain species of bacteria are more commonly found in aspirates of the jejunum taken from patients with bacterial overgrowth.
The most common isolates are:
• Escherichia coli
Many patients with chronic diarrhea have bacterial overgrowth as a cause or a contributor to their symptoms.Various mechanisms are involved in the development of diarrhea 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. SIBO can sometimes be triggered by an acute gastrointestinal infection.
Why SIBO Matters