In an article posted on May 28, 2008, New Scientist magazine says, "The good bacteria that inhabit our guts are more beneficial than we imagined. As well as crowding out dangerous organisms, they also release molecules that may protect us against inflammatory diseases, such as colitis."
Dennis Kasper at Harvard Medical School and his colleagues found that mice inoculated with Bacteroides fragilis - a human gut bug that produces a molecule called PSA - were able to fend off colitis provoked by the pathogenic bacterium Helicobacter hepaticus. Mice inoculated with strains that could not produce PSA, however, succumbed (Nature, vol 453, p 620).
PSA given orally also protected mice from colitis.
If it has a similar effect in humans, supplementary PSA could help treat inflammatory gut disorders.
Source: http://www.newscientist.com, From issue 2658 of New Scientist magazine, 28 May 2008, page 19.