May 11, 2004

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EFSA: Safety assessment of antibiotic resistance markers

Spain: No cultivation of Bt176 maize

At the end of April the new Spanish government announced a ban on the cultivation of the insect-resistant Bt176 maize from next year, because it contains a gene which confers resistance to the antibiotic ampicillin. The government based its decision on a recently published report from the European Food Safety Authority (EFSA).

It is highly unlikely that an antibiotic resistance gene from GM maize will be absorbed by micro-organisms

In this report the EFSA’s expert panel on genetically modified organisms had recommended that no new transgenic plants be approved if they contain genes conferring resistance to medicinally important antibiotics. This decision will not affect MON810 Bt maize, another variety grown in Spain.

EFSA’s GMO Panel believes that in general it is extremely unlikely that the cultivation and consumption of GM plants with antibiotic resistance genes will lessen the efficacy of the antibiotics in question. Nevertheless, the experts are recommending as a precaution that in future GM plants should no longer contain any genes which confer resistance to antibiotics that are still regularly used to treat infectious diseases in humans or animals.

Marker genes: Restricted use

The EU Deliberate Release Directive 2001/18, which has been in effect since October 2002, stipulates that the use of these marker genes should be gradually phased out. For this reason the panel felt it was important to take a close look at the safety of the different antibiotic resistance genes and has divided them into three groups.

• Group 1: No restrictions
  These genes confer resistance to antibiotics which are now of very limited relevance for human and animal medicine, in some cases because their side-effects are too serious. In addition, the resistance genes in this group are already widespread in nature. The experts see no scientific justification for banning their use in GM plants.
  This group includes the kanamycin resistance gene nptII and the hygromycin resistance gene hph. nptII is the most commonly used marker gene in GM plants.
• Group 2: Only for deliberate release trials
  These antibiotic resistance genes are also widespread in nature, but the corresponding antibiotics are still used to treat specific diseases. Only GM plants grown in temporary, geographically restricted field trials will be able to carry these resistance genes in the future, but not GM plants which are commercially grown.
  These kinds of markers include the resistance genes ampr (ampicillin) and CmR (chloramphenicol). Bt176 maize carries the ampr gene.
• Group 3: No longer permitted
  Marker genes in this group confer resistance to antibiotics that are highly relevant for human medicine. The experts therefore recommend that newly approved GM plants should not contain these resistance genes at all in future, regardless of how widespread they are in nature.
  This group includes the gene nptIII, which confers resistance to the reserve antibiotic amikacin and the tetA gene (tetracyclin).

Bt maize without resistance markers

The GMO Panel’s report should assist the European Commission and member states in future decision-making about approval applications for new GM plants. However, it does not call into question approvals that are already in force. Despite this the EFSA vote has prompted the Spanish government to ban the cultivation of Bt176 from next year.

Spain is currently the only country in the EU to grow transgenic plants on a large scale; 32,000 hectares in 2003, two thirds of which was Bt176 maize. In the past year another Bt maize (MON810) has also been growing on Spanish fields. This one is not affected by the ban because it contains no antibiotic resistance genes.