Antibiotics disrupt gut for longer than previously thought

[Guest guest]

From: binstock <binstock@...>

Study shows antibiotics disrupt gut

November 18, 2008

Helen Branswell

THE CANADIAN PRESS

<http://www.healthzone.ca/health/article/539233>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. "

-