SIBO

A case report by Kurtovic et al. (2005) describes a man who had been experiencing diarrhea and abdominal pain for 27 years.  He was diagnosed with SIBO by duodenal aspirates registering 10¹² CFU of bacteria/mL.  He was given antibiotics for four weeks, with no improvement in either symptoms or bacteria count.  Then he was given ten grams of lactulose twice a day for the next four weeks.  His symptoms disappeared after only three days on lactulose, and his bacteria count went down to 10⁷ CFU/mL.  They tried doubling the dose for the next four weeks but the count did not go down any further.  When he stopped taking the lactulose, his symptoms came back and by two weeks his bacteria count was up to 10¹¹ CFU/mL.  He went back on the lactulose long term and by the time of the report had been symptom free for six months.  The authors suggest that the mechanism by which the lactulose was suppressing his bacterial overgrowth was that the bacteria was fermenting it into short chain fatty acids, which are quite acidic, and thus their environment became less hospitable. 

Furnari et al. (2010) did a randomized controlled trial with 77 symptomatic patients who had tested positive for SIBO by a 50-g glucose breath test with a rise of 12 ppm within two hours.  Those with a basal hydrogen level above 10 ppm were excluded.  The participants were given rifaximin, either alone or with five grams of partially hydrolyzed guar gum (PHGG) each day for ten days.  A month after the end of the treatment they took the breath test again.  87% of those who stuck with the PHGG protocol tested negative, compared to only 62% of the control group (p = 0.017).  Symptoms were also improved to a greater degree by the PHGG, although this was not statistically significant.  The authors suggest that the mechanism by which the PHGG improved the results of the treatment was by increasing intestinal motility and thus carrying the bacteria through the intestines to be removed.  They also mention that it leads to increased populations of lactobacilli and bifidobacteria in the colon, as well as increased levels of acetate, which is a source of energy for colonocytes, and they mention that when these species are reduced, there are less short chain fatty acids, resulting in a higher pH, which favors bacterial overgrowth. 

References:

Furnari, M., Parodi, A., Gemignani, L., Giannini, E. G., Marenco, S., Savarino, E., Assandri, L., Fazio, V., Bonfanti, D., Inferrera, S., & Savarino, V. (2010). Clinical trial: the combination of rifaximin with partially hydrolysed guar gum is more effective than rifaximin alone in eradicating small intestinal bacterial overgrowth. Alimentary Pharmacology & Therapeutics, 32(8), 1000–1006. 

Kurtovic, J., Segal, I., & Riordan, S. M. (2005). Culture-proven small intestinal bacterial overgrowth as a cause of irritable bowel syndrome: response to lactulose but not broadspectrum antibiotics. Journal of Gastroenterology, 40(7), 767–768.