Gut Bacteria and Irritable Bowel Syndrome

Bacteria are present in the normal gut (intestines) and in large numbers the lower parts of the intestine. They achieve concentrations of several billion in the colon. These "normal' bacteria have important function in life:

• They protect against infection by "bad", or pathogenic, bacteria
• They help the immune system of the gut to develop
• They produce a variety of substances, including some essential vitamins, that have an important nutritional value

Together, the normal bacteria are often referred to as the gut flora. A variety of factors may disturb the mutually beneficial relationship between the flora and its host, and disease may result. For example, temporarily suppressing the normal flora in the colon can be a side effect experienced by a susceptible person after taking a course of antibiotics to treat an infection. This then provides the opportunity for bacteria that can cause disease to take hold.

Many consider a different disturbance in the interaction between the flora and the host to be the fundamental cause of ulcerative colitis and Crohn's disease. In these instances, the type or quantity of bacteria in the gut may not be abnormal' Instead of peaceful and mutually beneficial coexistence, the host responds to the normal bacteria as if they were disease causing. The result is intense inflammation.

Do Bacteria Play a Role in IBS?

The possibility that gut bacteria could have a role in irritable bowel syndrome (IBS) may surprise some; there is indeed, now quite substantial evidence to support the idea that disturbances in the bacteria that populate the intestine may have a role in at least some patients with IBS. What is this evidence? It can be summarized as follows:

1. Surveys which found that antibiotic use, well known to disturb the flora, may predispose individuals to IBS,
2. The observation that some individuals may develop IBS suddenly, and for the first time, following an episode of stomach or intestinal infection (gastroenteritis) caused by bacterial infection,
3. Recent evidence that a very low level of inflammation may be present in the bowel wall of some IBS patients, a degree of inflammation that could well have resulted from an abnormal interaction with bacteria in the gut,
4. The suggestion that at IBS may be associated with the abnormal presence, in the small intestine, of types and numbers of bacteria that are normally found only in the large intestine: a condition termed small intestinal bacterial overgrowth (SIBO),
5. Accumulating evidence to indicate that altering the bacteria in the gut, by antibiotics or probiotics, may improve symptoms in IBS'