Antibiotic resistance predates drugs – by 30,000 years-The New Scientist Mag

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Antibiotic resistance predates drugs – by 30,000 years
31 August 2011 by Bob Holmes


IN THE beginning there was antibiotic resistance. Bacteria have been carrying antibiotic-resistance genes for far longer than humans have had medical antibiotics. This fact - long suspected, and now proved - suggests that any antibiotic drug derived from a natural source is doomed to a short effective life.

Most antibiotics are developed from toxic molecules produced naturally by bacteria or fungi. This has led microbiologists to suspect that genes conferring resistance to these molecules must be a natural part of many microbes' genomes. Indeed, resistance genes have been found in bacterial samples taken from ancient sources such as permafrost. However, as with any study of ancient DNA, it has been difficult to prove that the samples are not contaminated with modern DNA.

Gerry Wright at McMaster University in Hamilton, Canada, and colleagues thought they could settle the question with samples from unusually pristine permafrost in the Yukon territory of Canada. Many permafrosts undergo freeze-thaw cycles over the millennia, but these samples have been continually frozen for 30,000 years, minimising the risk of recent DNA working its way in.

Wright's team took two cores from this permafrost and analysed DNA from the centre of each. The samples contained DNA from mammoths, bison and other species present at the site during the Pleistocene, but lacked detectable DNA from modern species such as spruce trees and moose, confirming that the DNA samples were truly ancient.

"The proof that the cores are not contaminated, and reflect the DNA from 30,000 years ago, is the best I've ever seen," says Christopher Walsh of Harvard University, who was not part of Wright's team.

With contamination ruled out, the researchers looked for a variety of bacterial antibiotic-resistance genes. Sure enough, they found several, including those for resistance to penicillin, tetracycline and vancomycin - conclusive proof that these genes truly pre-date medical antibiotics (Nature, DOI: 10.1038/nature10388). "This is just part of the natural history of the world," says Wright.

The results suggest that even the newest antibiotics are likely to be short-lived, since bacteria merely have to acquire resistance genes that already exist somewhere in nature - a much quicker task than waiting for new mutations to arise.

Researchers might find it more useful to focus on preventing the genes in soil bacteria from spreading into pathogens - a process about which relatively little is known, says Wright.