New EFSA report: Adverse effects from marker genes "unlikely"
The European Food Safety Authority (EFSA) has published a new scientific opinion on the potential health and environmental risks arising from the use of antibiotic-resistance genes as marker genes in genetically modified plants. A joint scientific opinion of EFSA’s GMO Panel and BIOHAZ Panel comes to the conclusion that, based on the current state of knowledge, adverse effects on human health and the environment resulting from the use of marker genes in genetically modified plants are unlikely.
In another scientific opinion, the GMO Panel has confirmed its earlier positive safety assessment of MON863 maize and the Amflora potato with modified starch composition developed by BASF, on the basis that there were no new scientific findings that would make a revision of the previous reports necessary. Both plants contain genes that confer resistance to the antibiotic kanamycin .
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The reason behind the new scientific assessment is that some genetically modified plants contain genes that confer resistance to the antibiotics kanamycin (nptII gene) and streptomycin (aadA gene). Both antibiotics are of clinical relevance in human and veterinary medicine. Kanamycin has been classed by the World Health Organization (WHO) as an ‘essential medicine’ for treating bacterial infections. The European Medicines Agency (EMEA) also sees kanamycin as an increasingly important reserve antibiotic, e.g. for treating tuberculosis. The opinions therefore focused on the question of whether these antibiotic‑resistance genes could be transferred from plants to bacteria (horizontal gene transfer) and what the consequence would be. One possible consequence would be a further spread of antibiotic-resistant pathogens. In 2004 the GMO Panel included the medical relevance of certain antibiotics as a criterion for assessing the safety of the use of the corresponding antibiotic-resistance genes in genetically modified plants. At the time, the GMO Panel considered kanamycin to be of only limited importance as an antibiotic in medical practice. |
Gene transfer frequency and the current spread of resistance genes are critical factors
However, the GMO Panel’s safety assessment was based on two more factors, which the new scientific opinion regards as critical: the probability of the antibiotic-resistance genes being transferred from a GM plant to bacteria, and the existing distribution of the corresponding resistance genes in the environment. Only if the resistance genes were transferred to bacteria often enough to cause a measurable increase in the number of resistant bacteria in the environment would this become a safety risk.
The scientific opinion once again establishes that kanamycin- and streptomycin-resistance genes are widespread in nature. Bacteria with these resistance genes can be found regularly in samples taken from hospitals, soil, rivers and lakes.
By comparison, the frequency of gene transfer from plants to bacteria is negligible. The opinion states that this kind of transfer has not yet been demonstrated under natural conditions or in the laboratory. The EFSA experts conclude that, based on current knowledge, the use of these resistance genes in GM plants cannot have an adverse effect on the effectiveness of antibiotics in medicine.
EFSA’s safety assessment is shared by Germany’s Central Commission for Biological Safety (ZKBS). In January 2009 the ZKBS published an updated assessment of antibiotic-resistance genes in genetically modified plants.
EFSA’s new report also points out that the kanamycin-resistance gene used in genetically modified plants is not contributing to the problems that have occurred with the treatment of tuberculosis. Kanamycin is an important reserve antibiotic for the treatment of tuberculosis, but more and more multiresistant pathogen strains are emerging around the world. Together with the European Medicines Agency (EMEA), the EFSA experts note that the nptII gene is not responsible for the current emergence of multiresistant tuberculosis pathogens.
Positive assessment not unanimous
However, the report also emphasises a few general imponderables in the risk assessment of antibiotic-resistance genes in transgenic plants. These arise from limited possibilities for taking samples and for establishing the source of transferable antibiotic-resistance genes.
In addition, two members of the BIOHAZ Panel expressed minority opinions. One of their concerns is that if a horizontal gene transfer event were to take place despite the extremely low probability, any adverse impacts on the environment and human health cannot be adequately assessed. In view of the divergent opinions, EFSA checked whether additional scientific research was necessary. The chairmen of the two panels indicated that the minority opinions had been taken sufficiently into account in the scientific opinion and that no further research was necessary.
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