Study: Antibiotic use may disrupt gut flora

6/22/2009

ANN ARBOR, Mich. Patients on a course of antibiotics may have disrupted gut flora for weeks after stopping the medication, according to a report in the June issue of Infection and Immunity.

It’s common knowledge that a protective array of bacteria can be found in our intestinal tracts. Antibiotics at least temporarily disturb that 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.

In studies in mice, University of Michigan scientists last week determined 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 eventually could lead to better choices of antibiotics to minimize side effects of diarrhea, especially in vulnerable patients. They also could aid in understanding and treating inflammatory bowel disease, which affects an estimated 500,000 to 1 million people, and Clostridium difficile, a growing and serious infection problem for hospitals.

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

Mice, which normally develop a diverse set of microbes after being born without one, were then 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,” Young said.

Although cefaperazone is not commonly used in the United States, such related drugs as cefoxitin are, Young said. The study findings suggested that it is very important to use antibiotics only when indicated, especially in people with health problems that might already compromise their gut microbe health. Multiple rounds of antibiotics also may deserve concern.

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