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Antibiotics promote C. diff infection by killing gut bacteria

The bacteria killed by antibiotic treatments are responsible for bile acids that prevent other infections.
By Stephen Feller   |   Jan. 6, 2016 at 4:04 PM

RALEIGH, N.C., Jan. 6 (UPI) -- Bacteria in the gut are involved in many of the body's functions, from the creation of neurons in the brain to regulating chemicals that help break food down.

Scientists at North Carolina State University found in experiments with mice that a single course of antibiotic treatment can open a window for Clostridium difficile, or C. diff, to thrive because bacteria responsible for altering bile acid were killed off, according to a new study.

Primary bile acids are made in the liver from cholesterol to aid in digestion and fat absorption, and in controlling lipoprotein, glucose, drug, and energy metabolism. The acids travel through the intestinal tract to the large intestine, where other bacteria convert them to secondary bile acids. These secondary acids inhibit the growth, and infection by, C. diff.

"These findings are a first step in understanding how the gut microbiota regulates bile acids throughout the intestine," said Casey Theriot, an assistant professor of infectious disease at North Carolina State, in a press release. "Hopefully they will aid the development of future therapies for C. difficile infection and other metabolically relevant disorders such as obesity and diabetes."

In the study, published in the journal mSphere, the scientists identified 26 primary and secondary bile acids in mice, defining their levels before and after treatment with an antibiotic.

The scientists then added C. diff spores to concentrations of the acids, finding primary bile acids allow spores to germinate, regardless of antibiotic treatment, which included the broad-spectrum antibiotics cefoperazone, clindamycin and vancomycin.

When the spores passed into concentrations that mimicked the large intestines of mice, altered secondary bile stopped C. diff from growing. When bacteria that turn primary bile acids into secondary acids had been killed during antibiotic treatment, C. diff was able to grow.

Scientists said the experiments showing the importance of gut bacteria to preventing at least one bacterial infection -- and how antibiotics can prevent the inhibition of its growth -- may help guide future research into preventing the infections.

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