ONE of the most convincing arguments levelled against genetically modified
crops is that the various genes in them that confer resistance to antibiotics
will spread into the environment, eventually making life-threatening bacteria
resistant to those drugs. But such doomsday scenarios look less convincing this
week, as British researchers report having tried and failed to get various
bacteria to take up such a gene from a commercial variety of GM maize.
John Heritage and his colleagues at the University of Leeds presented their
results in Scarborough at a meeting of the British Society of Animal Science.
The government-funded project is only halfway through and the researchers have
yet to publish their results in full. But they have so far drawn a blank in
experiments to see if bacteria pick up and activate bla, a gene in GM
maize which confers resistance to ampicillin, a commonly used antibiotic. The
researchers caution, however, that they still can鈥檛 rule out the scenario
altogether.
鈥淚t鈥檚 encouraging that a reputable scientist has studied the transfer of a
gene from GM maize to bacteria to gain actual data, rather than extending
speculations that such an event might occur,鈥� says Charles Arntzen, president of
the Boyce Thompson Institute for Plant Research in Ithaca, New York.
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Developed by the Swiss company Ciba-Geigy, now Novartis, the maize is
engineered to produce a bacterial toxin lethal to the European corn borer, a
major pest of maize. Unlike other GM crops, it also contains the bla
gene against ampicillin. The gene is not active in the plant, but the worry is
that gut bacteria might pick it up and activate it when the maize is fed to
animals.
Once in the environment, the bacteria might spread the same gene to
hospitals, making life-threatening bugs resistant to ampicillin and to related
penicillin-like antibiotics. Despite the fact that the bla gene is
already abundant in bacteria through medical overuse of ampicillin, opponents of
GM foods fear that the maize would exacerbate the existing problem.
Novartis sells the maize widely in the US, and in 1996 the European
Commission cleared it for sale in Europe, despite opposition from British
experts
(New 杏吧原创, 4 May 1996, p 7). But, two years later,
France鈥檚 highest court banned the sale and cultivation of the maize
(New 杏吧原创, 3 October 1998, p 5).
In his experiments, Heritage looked for evidence that gut bacteria from
chickens had accepted and activated the bla gene, after the birds had
been fed the GM maize for five days.
Heritage even served up the gene 鈥渙n a plate鈥� in plasmids, promiscuous loops
of DNA routinely swapped by bacteria. He added pUC18, the bla-bearing
plasmid used to produce the maize, to silage effluent and to saliva and rumen
fluid taken from sheep. 鈥淲e haven鈥檛 seen it taken up and activated by bacteria
in the normal flora of the rumen, saliva or silage yet,鈥� he says.
But these negative findings aren鈥檛 the end of the story, Heritage warns.
鈥淭hat doesn鈥檛 mean there aren鈥檛 conditions where it might be taken up and
activated.鈥� Next, he plans to test the fate of the bla gene when the
maize is fed to sheep.
鈥淚鈥檓 glad [the government] spent money investigating what was always a
speculative scenario,鈥� says Derek Burke, former chair of the British committee
that recommended Europe reject the maize. 鈥淚t now looks as though the risk is
less than was originally thought,鈥� he says.