Gut Reaction
A
ntibiotics save countless lives each year—but the
community of beneficial bacteria that live in human
intestines, known as the microbiome, frequently
suffers collateral damage.
Those friendly bacteria, which number in the trillions, specifi-
cally evolved with humans and help keep us healthy by doing things
like breaking down dietary fiber and competing for resources with
harmful bacteria. When the gut microbiome is upset by antibiotics,
the consequences, such as C. difficile infections, can be
life-threatening.
That’s why Peter Belenky, PhD, an assistant professor of
molecular microbiology and immunology at Brown, is trying to
find ways to minimize these side effects. In a recent study on mice,
he and his research team learned how antibiotics change the
makeup and function of the gut microbiome, and showed that a
mouse’s diet can affect those changes, for better or worse.
He hopes these findings eventually could help people who have
to take antibiotics. “Doctors now know that each antibiotic
prescription has the potential to lead to some very harmful
microbiome-related health outcomes, but they do not have reliable
tools to protect this critical community while also treating deadly
infections,” he says.
For the study, PhD student Damien Cabral treated three groups
of mice with different antibiotics, then watched how the mouse gut
microbiomes changed and adapted in response.
Amoxicillin, which is commonly used to treat ear infections and
strep throat, drastically reduced the kinds of bacteria in the gut and
changed the genes used by the remaining bacteria. Ciprofloxacin,
used for urinary tract infections, and doxycycline, often applied in
treating Lyme disease and sinus infections, had less pronounced
effects on the gut bacteria.
They also found that adding glucose to the mouse’s diet made
one particular type of beneficial bacteria more susceptible to
amoxicillin.
“For a long time we’ve known that antibiotics impact the
microbiome,” Belenky says. “We have also known that diet impacts
the microbiome. This is the first paper that brings those two facts
together.”
But he adds that since the study was done on mice, they still have
a lot to learn. Their ongoing research includes looking at how
different kinds of dietary fibers impact the microbiome after
antibiotic treatment.
“Now that we know diet is important for bacterial susceptibility
to antibiotics,” Belenky says, “we can ask new questions about
which nutrients have an impact and see if we can predict the
influence of different diets.”
HEALTH DISCOVERIES l WINTER 2020 7
Diet changes the sensitivity of the mouse microbiome to antibiotics. BY MOLLIE RAPPE