Courtesy National Institutes of Health
Bacteria are everywhere. Human intestines are loaded with bacteria (more than a trillion of them). Research findings are showing that humans have a symbiotic relationship with their intestinal flora. Our health depends upon certain bacteria in our gut.
Good bacteria help us digest our food, repress the growth of yeast and other harmful microbes, promote growth of cells lining the intestines, trains the early immune system in fighting harmful bacteria yet leaving the helpful species alone. Bacteria are also implicated in preventing allergies, an overreaction of the immune system to non-harmful antigens.
In a recent paper, Dennis Kasper at Harvard Medical School proposed
"that molecules of the bacterial microbiota can mediate the critical balance between health and disease" Nature: 29 May, 2008; A microbial symbiosis factor prevents intestinal inflammatory disease.
Bacteroides fragilis is a common bacterium found in the human gut that produces a molecule called Prostate Specific Antigen (PSA). Mouse studies suggest that PSA can influence the development of immune cells called T cells. Experiments in mice showed that PSA inhibited the production of chemicals by intestinal immune cells that usually trigger inflammation in response to infection with H. hepaticus. Read more about the study in New Scientist
I would like to challenge readers to answer this question using our comments feature, and to also suggest what you need to do to regain your "gut buddies".