A fast and sensitive test for detecting a potentially deadly strain of bacteria that contaminates food has been developed by scientists at the University of California, Davis. The researchers hope the procedure will eventually be used by food inspectors and processors to prevent food poisoning caused by the bacteria. The results of the study will be reported in the January issue of the Journal of Dairy Research, a British scientific publication. The new test targets a bacterium known as E. coli 0157:H7, which in 1993 caused the deaths of four children who ate under-cooked hamburgers from a fast-food restaurant in the Pacific Northwest. In recent months, the same food-borne bacterium has sickened more than 9,000 people in Japan, causing 11 deaths. "We are announcing the development of this diagnostic test now in hopes that it can be put to use worldwide as an early-warning system in combating food poisoning," said test developer Prabhakara V. Choudary, director of the UC Davis Antibody Engineering Laboratory. "We also hope that this discovery will encourage more people working with emerging technologies to get involved in solving this problem that concerns us all." E. coli 0157:H7 is estimated to cause 10,000 to 20,000 cases of infection in the United States annually, according to the federal Centers for Disease Control and Prevention. There are hundreds of strains of the bacterium Escherichia coli, most of which are harmless and live in the intestines of healthy humans and animals. E. coli 0157:H7, however, causes infections in people that often lead to bloody diarrhea and occasionally to kidney failure. Preschool children and the elderly are at the greatest risk of serious complications. Choudary, a molecular biologist credited with several accomplishments in recombinant DNA technology, and Christopher M. Gooding, a post-graduate researcher in the Antibody Engineering Laboratory, created the new test together. They developed the test for milk, ice cream and meat, and, in continuing research, also are tailoring it for use in seafood. Current procedures used for detecting bacterial contamination in food products rely on sampling the suspected bacteria, growing it in the laboratory and then analyzing it with immunoassays or recombinant DNA technology. These methods typically require at least two days to yield conclusive results. "Current techniques can provide speed or sensitivity, but not both," says Choudary. "The test we have developed can detect in just eight hours even one cell of the disease-causing bacteria from a sample of a food product. When dealing with the safety of the public food supply, this type of efficiency is critical." In designing this test, they first spiked samples of raw milk and commercially produced ice cream with E. coli 0157:H7 and allowed the bacteria to grow in the samples for several hours. To each bacteria-spiked sample, they add magnetized beads no larger than the point of a pin. The beads have been coated with antibodies, proteins designed to latch on to other specific proteins located on the surface of E. coli 0157:H7 cells. When mixed into the vial of each food sample, the antibody-coated magnetic beads grab hold of the targeted bacteria. A magnet is then placed next to the vial, pulling the beads and their captive bacteria to the side of the vial, while the remainder of the food sample is washed out of the vial. The researchers then put each sample of "captured" bacteria through a process known as PCR amplification, a procedure that allows them to make millions of copies of specific segments of the DNA. In addition to containing the basic genetic code for most life forms, DNA also serves as a handy form of identification. The researchers amplify segments of DNA that code for two genes specific to E. coli 0157:H7. These two genes produce the toxins in the bacteria that make them so harmful to humans. Choudary and Gooding then analyze those segments using a procedure known as gel electrophoresis to determine if they are indeed genes from the bacterium in question. "This method could benefit dairy producers as well as food inspectors, since the methodology is not technically demanding, and can be easily and rapidly performed by technical personnel with minimal training," said Choudary. He and Gooding hope to continue their research in this area to automate the testing procedure. The UC Davis Antibody Engineering Laboratory, directed by Choudary, is devoted to finding alternative hosts other than animals for large-scale production of antibodies and vaccines. This study was sponsored through the UC Davis-based California Institute of Food and Agricultural Research and was supported by a court-approved fund administered by the California Department of Justice and the Office of the Alameda County District Attorney.