Confirming fears of those opposed to genetic engineering, researchers in Great Britain reported this week that DNA from transgenic crops can find its way into the bacteria that dwell in the human intestines. In a study by scientists at the University of Newcastle, seven volunteers (all of whom had earlier had their lower bowels removed in unrelated surgeries) were given a single meal consisting of a burger and milkshake containing genetically modified soy. Intestinal bacteria from three of the seven volunteers later tested positive for trace levels of an herbicide-resistance gene from the soy. Although most GM material in foods is not thought to pose a risk to human health, many GM crops contain antibiotic-resistant marker genes as well, which critics fear could compromise the human immune system. Britain’s Food Standards Agency, which commissioned the study, dismissed such fears, saying the cross-over DNA was only found in trace levels, but Friends of the Earth said the report raised serious concerns about the safety of GM food and called for its withdrawal from the market until further testing could be done.