Commensal bacteria in the gut: learning who our friends are

Purpose of review Recent evidence has shown that commensal bacteria regulate intestinal physiology, development, and function. This review focuses on new insights into the effects of these organisms on health and disease. Recent findings Gastrointestinal tract development and function is determined by communication between the intestinal epithelium and commensal bacteria. Important regulatory interactions between these cells are being defined with early evidence indicating both beneficial and harmful consequences to the host. A subgroup of these bacteria overlaps with probiotic organisms that have preventative and therapeutic potential for diarrhea, inflammatory bowel disease (IBD), atopy, and other diseases, whereas evidence indicates some "nonpathogenic" commensal bacteria may promote an environment conducive to IBD, cancer, and other diseases. Summary Progress in understanding the relation between commensal bacteria and human health is likely to promote the identification of new approaches to disease prevention and treatment.