Science News June 18 talks of a study by a Cal Tech micro-biologist. "He and his colleagues showed that B. fragilis could prevent and cure IBD in animals...."
I did a quick google and found a study with what I THINK is a bad form of this bacteria. In the link below they say that
"In the IBD group, all the patients positive for ETBF had active disease, which suggests an association with disease activation or flare-up. ETBF was also found in patients with ulcerative proctitis, collagenous colitis, and microscopic colitis. In patients with Crohn disease, ETBF was usually seen in the colonic superficial inflammatory disease type. The presence of ETBF in IBD patients may represent alterations of endogenous bacterial flora, which may be related to either the etiology or flare-up of the disease or both. Colonization with ETBF may be acquired early in life or may be a de novo infection related to flare-ups of the disease. "
ETBF is enterotoxigenic Bacteroides fragilis
It's an old study 12 years I think
http://www.cdc.gov/ncidod/eid/vol6no2/prindiville.htm