A new study shows that the DNA of so-called "good bacteria" that normally live in the intestines may help defend the body against infection. The findings, available Oct. 2 online in the journal Immunity, are reported by Yasmine Belkaid, PhD, and her colleagues in the Laboratory of Parasitic Diseases at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
A person normally has 300 to 500 species of beneficial bacteria, known as commensals, in their intestines. These bacteria are not harmful and, in fact, help an individual maintain his or her digestive health. Typically, the immune system does not attack gut commensals, even though they are bacteria.
"Within the body of a healthy adult, microbial cells vastly outnumber human cells. Research to understand these microbial communities is an exciting scientific frontier," says Anthony S. Fauci, MD, NIAID’s director. "Among many opportunities related to the so-called 'microbiome,' targeting beneficial bacteria may offer new avenues for therapy against infectious and immune-mediated diseases."
Just how commensals protect against harmful bacteria, known as pathogens, is a complex question. "Pathogens often behave similarly to gut commensals," Belkaid says. Because the body needs commensals but also has to rid itself of disease-causing microbes, the immune system must distinguish the good bugs from the bad ones.
