New test detects pathogens in minutes

A new technique for detecting dangerous pathogens could lead to faster and cheaper diagnosis of disease and prevent food poisoning, say US researchers. The team claims their biosensor is accurate enough to identify different strains of disease-causing organisms in a blood sample in just 30 minutes, and at a fraction of the current cost. The researchers hope the test could soon be incorporated into an inexpensive hand-held device for use in the field and in the developing world.

Current biosensors rely on a costly and time-consuming technique called gene amplification, which involves taking a piece of DNA from the sample and adding enzymes to make enough copies to allow the pathogen to be detected. It can take up to 48 hours for a positive result. By contrast, the new process exploits a natural matching technique. A sample of the pathogen-containing material to be tested – blood or food, for example – is placed in a test tube and heated in the presence of an enzyme to break down the cells and release their genetic material. Then a dipstick is placed into the mixture and left for a few minutes. Like in a pregnancy test, if a red line appears, the particular pathogen is present. The process takes just half an hour from start to finish.

“Instead of taking many hours and costing several hundred dollars to be carried out in a specialist lab, the new test should be fully portable – the size of a cellphone – and cost just a couple of dollars for a fast result,” says team member Antje Baeumner, associate professor of biological and environmental engineering at Cornell University. “The idea is that it could be used directly in the field to sample meats and food products, or to test for diseases quickly and cheaply in cost-limited countries.” It works because the dipstick is impregnated with artificial cells containing sections of complementary DNA sequences which exactly match particular sections of RNA on the pathogen being tested for, along with a dye. So, if the RNA is present, it sticks to the dipstick DNA and the red dye is activated.

Lead researcher Sam Nugen designed computer software that selects sequences of complementary DNA to match the RNA from a range of pathogen bacteria, viruses and fungi, including E. coli, Streptococcus and the virus responsible for dengue fever. Biotech companies can then produce the required DNA sections in volume at low cost. Anything that speeds up the testing process will be welcomed, says Andrew Brabban, who carries out lab tests of beef for the deadly E. coli 0157:H7 at Evergreen State College in Washington, US. “Currently we have a ‘test and hold’ procedure, whereby meat is tested for E. coli and then the whole batch must be held back for about 24 hours until the test results come back. It costs time and money, so anything that’s faster, easier and costs less would be great,” he says.

The researchers hope to be able to multi-test samples for several pathogens soon. At the moment, they can detect the four different strains of the mosquito-borne dengue fever virus using several red bands on the testing dipstick. “And we’re working towards sequences for a full range of pathogens and detecting them at even lower concentrations. It would be great if this became a standard,” Baeumner told New Scientist. The study was presented on Monday at the Institute of Food Technologists Annual Meeting and Food Expo in New Orleans, US.

New Scientist
August 2, 2005

Original web page at New Scientist