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‘Good’ bacteria can switch sides, study shows

August 11th, 2009

Scientists have long known our bodies contain good bacteria that help us do things like digest food. But one such organism may also have the ability to protect germs that make us sick, a University of Louisville study has shown.

The finding is worrisome from a human health standpoint, said Michael Perlin, a UofL biology professor who led the study.

Perlin’s team found that a strain of E. coli bacteria that normally lives harmlessly in our digestive tract can mobilize to protect Salmonella, a microbe that often causes severe gastrointestinal illness.

“We knew some E. coli strains can leak a substance that makes even the sensitive E. coli cells around them survive exposure to antibiotics, but we didn’t know they could do the same for a totally different bacteria,” he said.

“This is something no one has seen before. It’s surprising and a little scary.”

An article on the discovery appeared Aug. 5 in the biology journal of the Proceedings of the Royal Society.

A large body of research has been devoted to understanding how bacteria become resistant to antibiotics by trading genes with other bacteria, Perlin said. The UofL study, however, identifies an entirely new way microbes can develop resistance.

Perlin’s team found that some bacteria act as “altruists,” sharing their resistance with other bacteria without transferring the responsible genes.

“This is of concern because it suggests that one type of bacteria that produces a substance to break down an antibiotic can protect other bacteria that cause diseases,” he said.

Antibiotic resistance has become a pressing public health problem, with the number of resistant bacteria increasing in the last decade. Many bacterial infections are becoming resistant to the most commonly prescribed antibiotic treatments, according to the U.S. Centers for Disease Control and Prevention.

National Institutes of Health figures show that about 90,000 people die each year due to a drug-resistant infection, up from 13,300 deaths in 1992.

UofL biologists Lee Dugatkin and Ron Atlas teamed up with Perlin to conduct the 3-year study funded by the National Institutes of Health.

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