Sources/Tips: Tips© February 2019


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

• Streptococcus

• Lactobacillus

• Bacteroides

• Enterococcusspecies

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



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