Antibiotics Take Toll On Beneficial Microbes In Gut

It’s common knowledge that a protective navy of bacteria normally floats in our intestinal tracts. Antibiotics at least temporarily disturb the normal balance. But it’s unclear which antibiotics are the most disruptive, and if the full array of “good bacteria” return promptly or remain altered for some time.

University of Michigan scientists have shown for the first time that two different types of antibiotics can cause moderate to wide-ranging changes in the ranks of these helpful guardians in the gut. In the case of one of the antibiotics, the armada of “good bacteria” did not recover its former diversity even many weeks after a course of antibiotics was over.

The findings could eventually lead to better choices of antibiotics to minimize side effects of diarrhea, especially in vulnerable patients. They could also aid in understanding and treating inflammatory bowel disease, which affects an estimated 500,000 to 1 million Americans, and Clostridium difficile, a growing and serious infection problem for hospitals.

Normally, a set of thousands of different kinds of microbes lives in the gut – a distinctive mix for each person, and thought to be passed on from mother to baby. The microbes, including many different bacteria, aid digestion and nutrition, appear to help maintain a healthy immune system, and keep order when harmful microbes invade.

“Biodiversity is a well-known concept in the health of the world’s continents and oceans. Diversity is probably important in the gut microsystem as well,” says Vincent B. Young, M.D., Ph.D., senior author of the study, which appears in the June issue of Infection and Immunity.

The study results suggest that unless medical research discovers how to protect or revitalize the gut microbial community, “we may be doing long-term damage to our close friends,” says Young, assistant professor in the departments of internal medicine and microbiology and immunology at the U-M Medical School.

Mice, which normally develop a diverse set of microbes after being born without one, then were given either cefoperazone, a broad-spectrum cephalosporin antibiotic, or a combination of three antibiotics (amoxicillin, bismuth and metronidazole). The scientists then observed what changes in the gut microbiota occurred immediately after the antibiotics were stopped or six weeks following the end of treatment.

“Both antibiotic treatments caused significant changes in the gut microbial community. However, in the mice given cefoperazone, there was no recovery of normal diversity. In other mice given the amoxicillin-containing combination, the microbiota largely recovered, but not completely,” says Young.

Funding for the study came from the National Institutes of Health.