'No risk to human health' from GM crop drug resistance

GM plants containing genes that make them 'immune' to antibiotics will not lead to a breed of 'superbugs' that we would be powerless to treat, say researchers in the October issue of The Lancet Infectious Diseases.

Antibiotic resistance genes, often referred to as 'markers', are used to prepare GM crops. Researchers who want to modify plants to become resistant to drought, for instance, will introduce the drought resistance gene and the antibiotic resistance gene together.

Not all attempts to modify the plants will be successful. To know which plants were modified, the researchers grow them in a mixture containing the antibiotic. Only those in which the genetic modification was successful — the plants that contain both the marker and the drought resistance gene — will survive.

Activists are concerned that if these markers 'leak out' of the GM plants, and are absorbed by bacteria, they could ensure the survival of the very bacteria the drugs were created to kill.

Philippe Gay, a retired scientist and former head of technology development and support at Novartis Seeds, and Stephen Gillespie, professor of medical microbiology at University College London, United Kingdom, reviewed what has been published so far on gene transfer.

They concluded from this study that it would be difficult for the resistance genes to jump from GM plants to bacteria. 

First, they say, once the plant cells come into contact with the bacteria, the plant DNA must be intact. Then, the plant DNA fragments that contain the resistance genes would have to physically meet up with the bacteria, and be integrated into the bacteria's own DNA, in such a way that the genes can function.

Gay and Gillespie say the probability of all of these conditions being met is very small.

They conclude that if the transfer were to happen at all, its effect would be insignificant compared with the resistance that arises through inappropriate medical prescriptions of antibiotics and from hospital environments.

However, the report adds that despite this conclusion, alternative markers should be developed as a precautionary measure.

Speaking to SciDev.Net, Nancy Terryn, of the Institute for Plant Biotechnology for Developing Countries at Ghent University, Belgium, agreed with the report. "There is no evidence that the antibiotic resistance genes used in approved GM crops pose a problem for human health," she said.

She also agreed that the use of different marker genes would be preferable. But, she adds, using antibiotic resistance markers are unavoidable in research on crops such as leguminous plants.

Mohamed A. Hamoud, professor of plant biotechnology at Tanta University, Egypt, notes that Gay and Gillespie only studied one resistance marker.

"Although [this marker] is one of the most frequently used, every marker must be evaluated on case-by-case basis," he told SciDev.Net.

Like Terryn, he agreed that since the report did not exclude the possibility that genes may transfer from GM crops to bacteria, "the development of 'clean', marker-free GM crops is the right way to ensure there is no risk to human health, and to gain public acceptance and compliance with regulatory requirements".

Many teams around the world are working on non-GM plants that are equally able to resist adverse conditions, such as pests, drought and high-salinity (see GM plant produces non-GM watermelon and Fungus is 'new tool for sustainable agriculture'). But Hamoud believes there is still a considerable amount of research that is needed in this area.

Link to abstract of paper in The Lancet Infectious Diseases *

Source: The Lancet Infectious Diseases, Volume 5, Issue 10 (October 2005)

Antibiotic resistance markers in genetically modified plants: a risk to human health?
Philippe B Gay, former head of Technology Development and Support, International R&D, Novartis Seeds
Professor Stephen H Gillespie, Professor of medical microbiology, University College London, London, UK

Summary

Cotransformation with an antibiotic-resistance marker is often necessary in the process of creating a genetically modified (GM) plant. Concern has been expressed that the release of these markers in GM plants may result in an increase in the rate of antibiotic resistance in human pathogens. For such an event to occur, DNA must not be totally degraded in field conditions, and the antibiotic-resistance marker must encounter potential recipient bacteria and be taken up by them, before being integrated into the bacterial genome, and the genes then expressed. In addition, the new recombinant must overcome the physiological disadvantage of acquisition of a piece of foreign DNA, probably in conditions where the new gene does not provide a selective advantage. We review each of these stages, summarising the investigations that have followed each of these steps. We contrast the potential increase in the antibiotic resistance reservoir created by antibiotic-resistance markers in GM plants with the current situation created by medical antibiotic prescribing. We conclude that, although fragments of DNA large enough to contain an antibiotic-resistance gene may survive in the environment, the barriers to transfer, incorporation, and transmission are so substantial that any contribution to antibiotic resistance made by GM plants must be overwhelmed by the contribution made by antibiotic prescription in clinical practice.

Access to full text + links: http://www.sciencedirect.com/science/journal/14733099

Copyright © 2005 Elsevier Ltd. All rights reserved