Science News - June 18, 2011

Both helpful and harmful microbes live in
human intestines. Some digest food or
prevent infections, while others are more
nefarious and can cause illness.

disease. Unfriending a bacterial buddy, even one that is sometimes disruptive, can have unforeseen and potentially unpleasant side effects.

Whether they’re helping or hurting, these trillions of tiny passengers are here to stay, so new research is mapping their preferred human habitats and figuring out what they do. Ultimately, understanding how bacteria operate inside their human hosts might reveal ways for humans to manipulate their own microbiomes to prevent or treat disease.

11/5/09). But even when bacteria are identified, it’s often not clear which are do-gooders and which are troublemakers.

“We’ve moved away from saying ‘ What are healthy bacteria?’ to ‘What are normal bacteria?’” says Julie Segre of the National Human Genome Research Institute in Bethesda, Md. Segre is one of the researchers taking inventory of the bacteria that grow on skin as part of the National Institutes of Health’s Human Microbiome Project. “Having acne — is it healthy? I don’t know, but it’s normal,” she says. The same goes for dandruff and other common microbe-related skin problems.

It may take a shift in the numbers of microbes in a mix to cause illness. Skewed microbial mixes have been fingered as contributors to obesity (SN: 6/17/06, p. 373) and high cholesterol. How much fat gets into the liver may also depend on the blend of bacteria in a person’s intestines, researchers at the University of North Carolina at Chapel Hill and colleagues reported in the March Gastroenterology.

In a study of bacteria inhabiting healthy
women’s vaginas, Jacques Ravel of the
University of Maryland School of Medicine
in Baltimore and his colleagues found
that each woman had one of five major
communities of microorganisms. Four
of the communities were dominated by
types of Lactobacillus, bacteria like those
found in yogurt that are well-known for
making infection-fighting lactic acid,
the researchers reported in the March
15 Proceedings of the National Academy
of Sciences.

Cross talk The human body has ways to communicate with its microbes. When helpful bacteria colonize intestinal cells (cell at left), the cells get a message to make compounds that help the bacteria attach (center). Sometimes pathogens overhear this chatter and horn in (right).