Friday, March 10, 2006
Is Irritable Bowel Syndrome a Bacterial Infection?
By: William E. Whitehead, Ph.D., Professor of Medicine and Co-Director, University of North Carolina Center for Functional GI and Motility Disorders
A recent article by Dr. Mark Pimentel and colleagues at Cedars-Sinai Medical Center caused a great deal of excitement because it suggested that irritable bowel syndrome is a bacterial infection that can be treated with antibiotics . These claims were widely reported in newspapers . If they are true, then the understanding and management of IBS will be revolutionized.
However, a careful reading of the study suggests caution. The authors made two important observations: first, that 78% of IBS patients had small bowel bacterial overgrowth and second, that eradication of bacterial overgrowth decreased the symptoms of diarrhea and abdominal pain and "cured" IBS in 48%. Let's take these observations one at a time. The patients who entered this study were not a representative group of IBS patients; they were patients who were referred for breath testing because their doctors suspected they had small bowel bacterial overgrowth. Selecting patients for testing in this way may have led to an overestimation of the proportion of IBS patients who have small bowel bacterial overgrowth. The only way to know what proportion of IBS patients have small bowel bacterial overgrowth is to test a large, representative group of patients.
The criteria for diagnosing small bowel bacterial overgrowth may also have been rather liberal. The investigators appropriately considered a test as positive only if they saw two peaks in breath hydrogen concentration, one representing intestinal bacteria and the second representing bacteria in the colon. However, they are unclear how high the first peak had to be for the test to be considered positive. Their rate of positive tests was much higher than expected; for example, out of 144 tests for suspected small bowel bacterial overgrowth carried out in our laboratory during a one year period, only 28% were positive. It is also difficult to evaluate the authors' claim that eradication of abdominal pain and diarrhea with antibiotics "cures" IBS because only 30% of the IBS patients treated with antibiotics returned for evaluation.
This was a retrospective study, so it was left to the discretion of the primary physician (not the investigators) which antibiotics were used to treat and whether the patient was asked to return for testing. It is important to know whether the other 70% were not sent back because they no longer had symptoms or whether they were not sent back because diagnosis and treatment of small bowel bacterial overgrowth made no difference, so their doctors had moved on to other tests. Quite apart from these concerns about the study design, there is a question whether these patients should be diagnosed as IBS. The Rome criteria  state that a patient should be diagnosed IBS if they have a sufficient number of a list of positive symptoms (which these patients had) and if there is no alternative, disease explanation for these symptoms.
Many gastroenterologists are aware that small bowel bacterial overgrowth can produce symptoms similar to IBS, just as inflammatory bowel disease and lactose malabsorption can; they do not label a patient as IBS if there is evidence for one of these alternative diagnoses. Although it is premature to conclude that the authors have found the cause and the cure for IBS, they have drawn attention to the fact that small bowel bacterial overgrowth is a relatively common condition that can cause symptoms suggestive of IBS. This may have the beneficial effect of causing physicians to consider this diagnosis more frequently, to test for it, and to treat appropriately when it is found.
However, antibiotics should only be prescribed when there is definite evidence of small bowel bacterial overgrowth because antibiotics occasionally cause harmful side-effects, and their indiscriminant use may lead to the development of antibiotic-resistant strains of bacteria. References:  Pimentel M, Chow EJ, Lin HC. Eradication of small intestinal bacterial overgrowth reduces symptoms of irritable bowel syndrome. Am J Gastroenterol 2000;95:3503-3506.  Beasley D. Study links intestinal bacteria to irritable bowel syndrome. Reuters, Los Angeles, December 13, 2000.  Thompson WG, Longstreth G, Drossman DA, Heaton K, Irvine EJ, Muller-Lissner S. Functional bowel disorders and functional abdominal pain. In: Drossman DA, et al. Rome II: The functional gastrointestinal disorders, 2nd edition. Degnon Associates, McLean, Va, 2000. Pp 351-432.
About IBS .
Probiotic bacteria helps irritable bowel syndrome 3/31/2005 -
A drink containing a probiotic strain isolated from infants relieved symptoms of irritable bowel syndrome to the same extent as pharmaceutical treatments for the condition, report Irish researchers. The team from the Alimentary Pharmabiotic Centre, set up last year at Ireland's University College Cork to investigate bacteria and gut health, found that patients who consumed a malted milk drink containing Bifidobacterium infantis 35624 everyday for eight weeks experienced fewer overall symptoms, abdominal pain and discomfort.
The symptom relief was comparable to that seen with Zelnorm (tegaserod) and Lotronex (alosetron), drugs that have been recently approved for the treatment of irritable bowel syndrome (IBS). IBS is a long-term condition that usually involves cramping, diarrhoea and constipation. It affects between 10 and 15 per cent of the Irish population and a similar proportion of people in other western countries. However the precise cause of IBS is not fully understood and there is no cure yet.
Treatments are aimed at alleviating symptoms but medication, for those with moderate to severe forms of the disease, does not work for all patients. Senior author on the new study, Professor Eamon Quigley, who is head of UCC's medical school, said the results "look very good in comparison to pharmacological products". "We believe we have very significant results. It is at least as effective as lots of available products, and probiotics have a good safety profile too," he told NutraIngredients.com.
In contrast, treatment with another probiotic bacteria, Lactobacillus salivarius UCC4331, also isolated at the Irish centre, appeared to have no more effect on IBS symptoms than a placebo drink. Both strains, patented by UCC, had shown interesting properties in laboratory studies.
“Previous studies of probiotic preparations have been small and used different probiotics, different doses and different definitions of IBS. Ours is one of the first properly powered trials conducted to accepted standards in this area,” Dr Quigley added. For the study, published in the March issue of Gastroenterology (vol 128, issue 3, pp541-51), 77 people with IBS were asked to drink a malted milk drink every morning. The drink either contained L. salivarius, B. infantis or no added bacteria. The subjects recorded their symptoms. “Our hypothesis is that low-grade inflammation is a factor in IBS and that certain probiotic bacteria can reduce this inflammation.
We have some evidence to support this theory because our paper shows a change in cytokine ratios after the probiotic treatment," said Dr Quigley. He added that further clinical trials are ongoing and research into the mechanism will also be carried out by the team. Neither of the strains is currently commercially available but the APC works in partnership with Procter and Gamble and is hoping to bring the bacteria to market in new products.