BACKGROUND & AIMS: Recently, a number of animal models for different aspects of 
inflammatory bowel disease (IBD) have been developed. The aim of this study was 
to use one of these to determine whether particular, ostensibly innocuous, 
intestinal bacteria could provoke or exacerbate IBD.
METHODS: Conventionally reared C.B17 SCID mice were compared with germ-free and 
gnotobiotic mice, monoassociated with 1 of 5 intestinal bacteria, after transfer 
of CD45RB(high) CD4(+) T cells from conventionally reared congenic BALB/c mice. 
Recipient mice were monitored over 7-12 weeks for clinical signs of IBD, and 
tissues were analyzed by histology/flow cytometry for abnormal inflammation and 
CD4(+) T cell outgrowth.
RESULTS: Neither germ-free mice nor mice monoassociated with segmented 
filamentous bacteria, Ochrobactrum anthropi, a nonpathogenic mutant of Listeria 
monocytogenes, or Morganella morganii developed any signs of IBD. In contrast, 
mice monoassociated with Helicobacter muridarum displayed an accelerated 
development of IBD in 5-6 weeks compared with 8-12 weeks observed in 
conventionally reared mice. The outgrowth of CD4(+) T cells in spleen and large 
intestine of H. muridarum monoassociated mice, as well as in conventionally 
reared mice was significantly higher than that in the other monoassociated mice.
CONCLUSIONS: Among the intestinal bacteria tested, H. muridarum can serve as a 
provocateur of IBD in this model.