If you had a sample of bacteria taken from an environmentally sensitive area, or from a patient with a severe infection, would you be able to tell if any of these bacteria had been genetically engineered? A group at Lawrence Livermore National Lab (LANL) is developing a technique for distinguishing natural DNA from DNA sequences designed in a lab. There is no general, intrinsic property that distinguishes artificial from natural DNA, so you have to tackle this problem by brute force. The LANL group scanned nearly 4000 DNA synthetic vector sequences - the basic DNA tools of genetic engineering, which have a mix of natural and human-designed DNA, looking for short segments of vectors that are not in any known natural bacterial DNA source. Their idea is to use these short, artificial segments to design probes for a DNA chip. With this DNA chip, you can test bacterial samples to see if they contain any artificial sequences, matching the chip probes - a fairly quick and easy way to find genetically engineered bacteria. The downside is that the chip is only as good as index of artificial sequences - the LANL group tried to be fairly comprehensive, but their list of 4000 sequences would need to be continually updated, with new chips designed on a regular basis. It's a great idea in principle, and as genetic engineering becomes easier, cheaper, and more widespread, we'll need tools like this. But it's important to keep things in perspective: in terms of threats to your health, there are far, far more harmful natural DNA sequences out there than genetically engineered ones. "DNA signatures for detecting genetic engineering in bacteria," Allen, et al., Genome Biology 2008, 9:R56 doi:10.1186/gb-2008-9-3-r56