Researchers Find Antibiotic Resistance in Ancient DNA
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An analysis of 30,000-year-old bacteria whose DNA has been recovered from the Yukon permafrost shows that they were able to resist antibiotics.
Antibiotics, before they became used as drugs, were natural products. The new finding is the first direct evidence that antibiotic resistance is a widespread natural phenomenon that preceded the modern medical use of antibiotics.
Experts had long predicted this on theoretical grounds, but they say the new finding underlines the need to use antibiotics sparingly, given that the genes for antibiotic resistance are ubiquitous and can easily be promoted by antibiotics.
"The fact that the genes for resistance are so ancient and widespread means there is no easy solution to the problem of resistance -- we will never invent a super-antibiotic that clears everything up," said Martin J. Blaser, a microbiologist at New York University.
DNA from the ancient bacteria was analyzed by Gerard D. Wright of McMaster University in Ontario. A colleague who works on ancient DNA, Hendrik N. Poinar, told him of a site at Bear Creek in the Yukon Territory in Canada where ancient DNA could be found uncontaminated by anything from the modern world.
Dr. Wright's team gathered DNA from a layer of mud about 20 feet beneath the surface. The mud was once the sediment around the edge of an ancient lake. Right above the mud layer lies a layer of volcanic ash deposited 30,000 years ago. The site had evidently been shielded from contamination because it contained DNA from ice-age animals like the mammoth, and none from contemporary species like elk or moose.
The ancient bacteria in the sediments turned out to contain all the major genes that enable modern bacteria to resist antibiotics, Dr. Wright reports in Thursday's issue of the journal Nature. He and his team grew the products specified by some of these ancient genes, showing that the resurrected proteins conferred resistance to antibiotics.
Antibiotics are substances produced by fungi, algae and bacteria for signaling and for defense. The inhabitants of this microbial world have also evolved genes that counteract antibiotics. After millions of years of chemical warfare, two classes of sophisticated genes have emerged, those that make antibiotics and those that provide resistance to antibiotics.
"Antibiotic resistance is part of the natural ecology of the planet, and this finding is a cautionary note about how we use these things," Dr. Wright said. "Antibiotics are remarkable resources that need to be carefully husbanded."
First Published September 1, 2011 12:00 am
