Antibiotic Overuse May Be Bad for Body's Good Bacteria

Aug. 24, 2011 -- Antibiotic overuse doesn’t just lead to drug-resistant superbugs, it may also permanently wipe out the body’s good bacteria. 

Good bacteria in the gut help people in many ways, including helping make vitamins and boosting immunity. Some researchers think that killing them off with antibiotics may be contributing to rises in chronic health conditions such as obesity, asthma, and cancer.

A commentary published in the latest issue of Nature calls for more careful prescribing of antibiotics, particularly in pregnant women and babies, who are just establishing their colonies of good bacteria in the gut. The commentary was written by Martin Blaser, MD, who heads the department of medicine at New York University’s Langone Medical Center.

Growing Antibiotic Use

Blaser points out that in a developed country like the U.S., the average child gets 10 to 20 courses of antibiotics by age 18.

Blaser says there’s no question that antibiotics, when given appropriately, save lives.

But they're not always used appropriately. Studies have shown that doctors often prescribe antibiotics before they know whether an infection is viral or bacterial. If the problem is a virus, antibiotics don't help.

For example, a 2003 study published in the Journal of the American Medical Association showed that doctors prescribed antibiotics for more than 60% of adults with upper respiratory tract infections, which are usually caused by viruses.

And a 2010 study published in Infection Control and Hospital Epidemiology found that doctors sometimes kept patients on antibiotics even after tests showed they had viral infections.

Disappearing Bacteria

As antibiotic use has increased, studies have shown that the kinds of bacteria that we live with are changing.

Blaser says he thinks some bacterial species that live in our bodies are going extinct. He points to the example of H. pylori, the bacterium best known for causing ulcers.

One hundred years ago, H. pylori was the main microbe that people carried in their stomachs.

Today, studies show that less than 6% of children born in the U.S., Sweden, and Germany carry that organism. That shows that the species is disappearing from its human hosts.

The health consequences of that aren't clear. Neither is the reason for the disappearance.

Blaser's point is that if one species of gut bacteria is disappearing, others are, too.

“We know there are impacts” from antibiotic use, “impacts we don’t even have the tools yet to study,” says Lita Proctor, PhD, who coordinates the Human Microbiome Project at the National Institutes of Health.

Links to Chronic Disease

Blaser says it’s clear those impacts go far beyond infections.

Farmers, for example, discovered decades ago that animals fed small amounts of antibiotics, below the doses used to treat infections, gain more weight.