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
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
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
pathogens overhear this
chatter and horn in (right).
Meet your microbiome
Researchers are just beginning to compile a Who’s Who of human-inhabiting
microbes (SN: 12/6/08, p. 11; SN Online:
June 18, 2011 | SCIENCE NEWS | 27