15 September 2010

Study Shows Repeated Antibiotic Use Alters Gut's Composition Of Beneficial Microbes

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Repeated use of an antibiotic that is considered generally benign, because users seldom incur obvious side effects, induces cumulative and persistent changes in the composition of the beneficial microbial species inhabiting the human gut, researchers at the Stanford University School of Medicine have found.
By a conservative estimate, something like 1,000 different varieties of microbes coexist harmoniously within a typical healthy person's gut, said David Relman, MD, professor of medicine and of microbiology and immunology at the medical school and chief of the infectious diseases division at the Veterans Affairs Palo Alto Health Care System. Relman is the senior author of a paper, which appears online in Proceedings of the National Academy of Sciences.

The study examined the effects of ciprofloxacin (trade name Cipro), an antibiotic that is widely prescribed for intestinal, urinary and a variety of systemic infections. In an earlier, short-term study, Relman's group had concluded that people's intestinal microbial communities seem to bounce back reasonably well within weeks after a five-day regimen of ciprofloxacin. This new study involved two courses of antibiotic administration, six months apart, and it revealed more-subtle, long-term effects of ciprofloxacin use - such as the replacement of multiple resident bacterial species by other, closely related varieties and the occasional complete eradication of a species.

The infrequent occurrence of easily visible side effects such as bloating and diarrhea from ciprofloxacin use has given rise to an assumption that the drug spares most beneficial gut-dwelling bacteria. Overall similarities between pre-regimen gut bacterial strains and their post-regimen replacements explain why such side effects aren't typically seen after ciprofloxacin use. Still, the more nuanced differences between the pre-existing communities and those that appear in the wake of this repeated disturbance present a new set of problems, said Relman, who is also the Thomas C. and Joan M. Merigan Professor at the medical school. A bacterial species whose presence was lost or diminished may have been performing a valuable job - for example, secreting a protein that's toxic to a particular pathogen - that is shirked by its replacement. The abandoned function might not be noticed until, perhaps, years later when the pathogen in question invaded the person's gut.

(Medical News Today)

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