LAST week opponents of genetic engineering seized on a report suggesting that DNA from GM food can enter bacteria in the human gut. Here at last was proof, they claimed, that antibiotic-resistant superbugs could emerge by picking up the marker genes found in some GM crops. So should we be worried?
鈥淲e鈥檝e said time and time again there鈥檚 a risk of this happening. Now they鈥檝e looked just once and they鈥檝e found it,鈥� says Adrian Bebb of Friends of the Earth. But most microbiologists, including the researchers at the University of Newcastle upon Tyne who did the study, dismiss such concerns.
In one of a series of studies for Britain鈥檚 Food Standards Agency, Harry Gilbert鈥檚 team at Newcastle fed burgers and milkshake containing GM soya to 12 healthy volunteers and to seven volunteers who鈥檇 had their colons surgically removed. By examining stools from the healthy subjects and material from the others鈥� ileostomy bags, the researchers could see how different parts of the digestive system affected DNA in the GM soya, which has a gene that makes it resistant to the herbicide glyphosate.
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The team found no trace of DNA from the soya in the stools of the volunteers with intact digestive systems. But they found that up to 3.7 per cent of the soya DNA remained in the contents of the bags. When they grew bacteria from these samples, they were able to detect trace amounts of the GM DNA using a technique called PCR.
That suggests a very few bacteria had taken up a foreign gene or transgene from the soya food.
Previous studies have suggested this is possible (New 杏吧原创, 30 January 1999, p 4) but it has never been directly demonstrated before. However, the Newcastle team wasn鈥檛 able actually to isolate any bacteria containing the soya transgene. Nor was there any evidence that the gene had actually started to function in the bacteria, they say.
The researchers conclude that while some DNA might survive as far as the small intestine, in people with normal digestive tracts it鈥檚 all broken down on the way through the colon. Even if some bacteria take up some of the DNA, they don鈥檛 make it out the other end. 鈥淲e have no evidence this has any adverse effects on humans,鈥� says team member John Mathers.
But Bebb points out that while the soya didn鈥檛 contain antibiotic resistance genes, other GM crops do. These marker genes are used during the creation of GM plants to reveal which cells have taken up the new bits of DNA.
However, Karen Scott of the Rowett Research Institute in Aberdeen has tried and failed to get human gut bacteria to take up ampicillin resistance genes, which are present in some GM crops. What鈥檚 more, she has found that such resistance genes are already widespread in the gut bacteria of many animals. This is probably because of the misuse of antibiotics in agriculture and medicine.
So even if gut bacteria did acquire and turn on antibiotic resistance genes from GM food, they would be a drop in the ocean of existing resistant bacteria. 鈥淢y opinion is that it鈥檚 not an issue,鈥� Scott says.
Despite the fact that the risks are so low, groups such as Britain鈥檚 Advisory Committee on Releases to the Environment recommend that no antibiotic resistance genes should be incorporated in new GM crops.