According to biotech critics, genetically modified crops carry insidious hitchhikers in the form of antibiotic resistance genes. Activists argue that the genes could somehow move into pathogenic bacteria, rendering antibiotics ineffective and thereby eliminating an important weapon in medicine's arsenal against disease.

Molecular breeders include selectable markers--conferring resistance to drugs such as kanamycin and streptomycin--with beneficial genes they introduce into pet plants such as soybean. Drug resistance acts as an initial screen: By incorporating the appropriate antibiotic in growth medium used to regenerate plantlets, scientists weed out untransformed tissue. Hopefully, the transgenic plants also carry the beneficial gene, say for enhanced ß-carotene content.

Scientists generally scoff at the possibility that resistance markers are a health menace, and point to the real threat posed by unwarranted prescription of antibiotics for minor viral infections and drug supplements in animal feed.1 Still, ag biotech companies increasingly edgy over consumer concerns about product...

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