Antibiotics disrupt gut for longer than previously thought

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Study shows antibiotics disrupt gut

November 18, 2008

Helen Branswell

THE CANADIAN PRESS

http://www.healthzone.ca/health/article/539233

This is your gut. This is your gut on drugs.

A new study reveals that a common antibiotic disrupts normal bacterial

levels in the digestive tract of healthy adults for longer than

previously thought. Six months later, in fact, some beneficial types of

bacteria were still wiped out or remained at levels lower than before the

drugs were taken.

" You don't want to be giving readers the impression that we

shouldn't be using antibiotics (when needed), " says Dr.

Relman, senior author of the study, which was published Tuesday in the

journal PLoS Biology.

" But it's the flip side. It's the trade-off part. . . . Because we

do overuse antibiotics. "

Relman, an infectious diseases specialist at Stanford University and the

Veteran Affairs Hospital at Palo Alto, Calif., conducted the study with a

team of colleagues. Funding for the work came from the Doris Duke

Charitable Foundation and the U.S. National Institutes of

Health.

Antibiotics aren't a targeted treatment. The drugs don't zero in on the

bacteria you want to kill and leave intact the rest of the body's normal

and healthy bacteria. That's why taking antibiotics to cure one problem

can give rise to another – for instance yeast infections or C. difficile

diarrhea.

But it's not clear just how much damage the drugs wreak on the body's

bacterial " flora " – the beneficial bacteria that inhabit places

like the gut, helping to keep us healthy and safe from bugs that would

make us ill.

To try to quantify the effect, Relman and his colleagues gave three

healthy volunteers – two men and a woman – a single course of the

antibiotic ciprofloxacin.

While all antibiotics will knock out a range of bacteria, cipro is

believed to be among the least disruptive of the drugs.

In fact, more than 30,000 U.S. postal workers were prescribed

ciprofloxacin in 2001 after letters containing anthrax were processed

through several sorting stations. There were few reports of postal

workers suffering side-effects from the drug, Relman said.

In this study, the researchers collected stool samples from their

volunteers before they started the five-day course of cipro, during

treatment and for months after.

They are actually still studying these individuals plus four others and

have samples going out a year after the first dose of the drug. But in

this paper they report on results for the first six months only.

They mined the stool samples for traces of bacteria using a technique

called polymerase chain reaction or PCR, identifying DNA from between

3,300 and 5,700 different types in the samples collected before

treatment. Most of the bacteria – in fact 93 per cent – haven't yet been

identified, Relman said.

The diversity in bacterial types was cut by about a third after the

volunteers took the antibiotics. Relman said the size of the reduction

came as a surprise.

" We find that cipro was more disruptive than we had thought....

About 30 per cent of all of the strains and species that we could see

were disrupted. And most of them were ... either knocked out or knocked

down. "

By four weeks post-treatment, most of the bacterial populations seemed to

have recovered, though some were still at depressed levels. And some were

not evident at all.

Given that so little is known about most of the bacteria, the researchers

can only hazard guesses at whether that effect would have any long-term

impact on the health of their volunteers. In the short term, none

reported feeling ill.

But these volunteers were healthy. If they were people already fighting

some infection or illness, the results might have been different. And

even with the healthy people, Relman said it's too soon to say there is

no health cost.

" The things that we see getting knocked out or knocked down are

typically associated with (good) health, " he said.

" We can't say that each and every one of these individual organisms

is necessary or important somehow or contributing to health ... But the

overall communities are associated with a lot of beneficial features for

the host. So the net effect could potentially be harmful. "

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doi=10.1371/journal.pbio.0060280http://biology.plosjournals.org/perlserv/?request=get-document & doi=10.1371/journal.pbio.0060280 & ct=1Free AccessStudy shows antibiotics disrupt gut