Probiotics and Inflammatory Bowel Disease
Definition of Probiotics - Probiotics are live microbial food ingredients that alter the enteric microflora and have a beneficial effect on health.
The gut flora consists of over 400 different species and is relatively stable throughout life, but is distinct in different individuals. These bacteria contain many enzymes whose activity is such that metabolic transformations in the bowel may rival the importance of those in the liver. Whilst the effect of this metabolism is generally beneficial producing for example vitamins and nutrients (short chain fatty acids) and breaking down carcinogens, under certain circumstances the flora may cause disease when the numbers of certain pathogenic bacteria such as clostridium defficile increase.
A number of observations suggest the bowel flora may be important in causing IBD. Gut lesions have been shown to be most frequent in the areas of highest bacterial concentration. If the faecal stream is diverted disease affecting the bowel further down may heal. Furthermore, lesions of Crohn's disease may be induced by instillations of faecal content to apparently unaffected loops of bowel. The gut mucosa produces antibodies that coat as much as 80-100% of normal bacteria in IBD but less than 20% in healthy controls. Finally rats and mice which have been bred lacking certain anti-inflammatory cytokines such as IL-10 will spontaneously develop colitis but only if bacteria are present in the gut.
For these reasons modification of the activity of the gut flora has been investigated as a way of controlling IBD. Antibiotics such as ciprofloxacin and metronidazole may prove very helpful but cannot be used for long periods because of the risk of bacterial resistance developing. As discussed elsewhere the effectiveness of enteral feeds (highlighted link) may be due to their reducing the metabolic activity of gut bacteria. Probiotics may prove beneficial by displacing other pathogenic bacteria or by promoting healthier metabolic pathways. They have not yet been widely used in IBD because the anti-inflammatory activity seems modest. A strain of Lactobacillus salivarius appears to improve colitis in IL-10 deficient mice. A non-pathogenic strain of E. Coli was reported to be as effective as mesalazine in UC. VSL-#3, a cocktail of eight strains of bacteria has been shown to be highly effective in patients with pouchitis.
In the future it seems likely that vigorous attempts will be made to find suitable probiotic organisms for the treatment of IBD. Apart from a search for new strains and more complex mixtures of different bacteria, genetically engineered organisms may be developed, possibly containing anti-inflammatory molecules such as IL-10. However, there is still considerable work to be done before probiotics can be considered as part of the standard treatment of IBD.