A recent study out of the University of Michigan Medical School suggests that the stomach bacterium Helicobacter pylori protects against inflammation caused by Salmonella in a mouse model of Inflammatory Bowel Disease (IBD).
This is surprising for two reasons: 1) IBDs occur primarily in the colon while H. pylori is active in the stomach, and 2) the H. pylori bacterium is regarded as dangerous gut flora and typically treated with antibiotics to avoid the development of stomach ulcers.
The findings of Higgins et al are equally unsurprising given the light that has been shed on helpful bacterial/parasitic gut balance by the Hygiene Hypothesis. The Hygiene Hypothesis suggests that a modest intestinal hookworm population may stave off the excessive inflammatory response inherent to Crohn's disease, Lyme disease, asthma, rheumatoid arthritis and other conditions. If this parasite whose reputation is built from its roles in epidemic illnesses in countries where sanitation is poor can, in small doses, help defend inflammatory diseases, then why couldn't the H. pylori bacterium as well?
There are currently no reports of an additive or destructive effect of both H. pylori and hookworm on gastrointestinal inflammation in humans, although it would be quite telling to see the results of their coincidence. Patients from many H. pylori studies have been excluded from reports because they also shown signs of hookworm-related anemia (Vijayan et al 2007, as an example). But this scientists wonders, because humans evolved almost symbiotically with both of these flora, if all of our immune systems would be better balanced were we not to wipe them both out completely.
A few thoughts from Dr. Higgins, one of the Salmonella study's researchers, can be found in an interview here.
Higgins PD, Johnson LA, Luther J, Zhang M, Sauder KL, Blanco LP, & Kao JY (2010). Prior Helicobacter pylori infection ameliorates Salmonella typhimurium-induced colitis: Mucosal crosstalk between stomach and distal intestine. Inflammatory bowel diseases PMID: 20976712