- NEW ORLEANS -- The increasing
use of antibiotics to treat disease may be responsible for the rising rates
of asthma and allergies. By upsetting the body's normal balance of gut
microbes, antibiotics may prevent our immune system from distinguishing
between harmless chemicals and real attacks.
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- "The microbial gut flora is an arm of the immune
system," says Gary Huffnagle at the University of Michigan in Ann
Arbour. His research group has provided the first experimental evidence
in mice that upsetting the gut flora can provoke an allergic response.
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- Asthma has increased by around 160 per cent globally
in the last 20 years. Currently about a quarter of schoolchildren in the
US and a third of those in the UK have the condition, but pinning down
the causes of the rise has proved difficult. Some researchers have blamed
modern dust-free homes, while others have pointed to diet.
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- Antibiotics have been implicated by some epidemiological
studies. For example, the rise in allergies and asthma has tracked widespread
antibiotic use. Furthermore, research in Berlin, Germany, has found that
both antibiotic treatment and asthma were low in the east compared to the
west when the wall came down.
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- As antibiotic use has increased in the east though, so
has asthma. This study is particularly valuable because the politically
divided populations were genetically very similar and enjoyed much the
same menu.
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- Fungal spores
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- Now Huffnagle has presented experimental evidence to
back up the case. His team gave mice a course of antibiotics before feeding
some of them with a yeast which is commonly found on human skin.
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- With the natural gut bacteria suppressed by the drugs,
the yeast became established in the mouse, with no side effects. Over the
course of the following two weeks, the researchers treated all the mice
with spores from a common fungus. Again, this does not cause disease, but
fungal spores can trigger allergies in people.
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- The mice whose gut flora had been manipulated, experienced
a much higher immune response to the spores, suggesting that changes to
the collection of microbes in people's guts following antibiotic treatment
might also make us more susceptible to allergies. "Suddenly, your
ability to ignore a mould spore has gone," Huffnagle told New Scientist.
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- The team has repeated the experiments with a second strain
of mice to show that the effect is not dependent on a particular set of
mouse genes. They have also used a different molecule to produce the allergic
response - an egg protein from chickens called ovalbumin that is commonly
used in allergy research.
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- In this case, when the team looked at the animals' lung
linings under a microscope the effect of the over-active immune response
was striking. "Their lungs are shredded, absolutely shredded. I'm
sure they can't breath," says Huffnagle.
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- Training regime
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- He speculates that our gut bacteria are somehow involved
in training the immune system to ignore harmless molecules that wind up
in our stomach. Precisely how they do this is a mystery though.
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- "He's on to a very special track," says Juneann
Murphy an expert in stomach bacteria at the University of Oklahoma in Oklahoma
City. "No one else has been able to make the connections before."
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- She says the findings reinforce the message that antibiotics
should be used only when absolutely necessary. She also suggests that patients
who have just finished antibiotic treatment should also receive "probiotic"
tablets containing "good" gut bacteria.
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- Eating foods such as raw fruit and vegetables also helps
to restore the natural balance in our guts. "Once you are done with
the antibiotics you are not finished," adds Huffnagle. "You need
to recover from the treatment itself."
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- The research was presented at the American Society for
Microbiology general meeting in New Orleans on Wednesday.
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