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INSTANT E.COLI TEST By Sean Henahan, Access Excellence
(Graphic: depicts sensor binding and activation) The E. coli strain 0157:H7 was responsible for recent illness and deaths in the United States involving fruit drinks and fast-food hamburgers. The same strain also caused an outbreak of food poisoning in Japan, and a current outbreak in Scotland that is linked to 10 deaths. The best test available up until now required the use of tissue culture and a wait of at least 24 hours. The new test involves a nice combination of basic biology and high-tech sensors. The working part of the sensor consists of a single molecule fabricated into a thin film. This molecule has a two-part composite structure. The surface of the molecule binds the bacteria, while the backbone underlying this surface a color-changing signaling system. "We have made synthetic surfaces that mimic the unique cellular binding sites for the toxins produced by E. coli 0157:H7 interactions. When these toxins are produced, they hunt around for places to bind. When they find the right receptor site, they attempt to bind. This activity in humans causes disease. In the sensor, it is what triggers the color change." explained Raymond Stevens, a chemist at the Ernest Orlando Lawrence Berkeley National Laboratory where the test was developed. The backbone of the sensor molecule is composed of a long diacetylene lipid, a molecule similar to the phospholipids that are the building blocks for cell membranes. Exposure to UV light links the molecules together by activating a triple bond within the diacetylene lipids, creating a blue-tinted polydiacetylene (PDA) film. PDA films are sensitive to changes on their surface as manifested by the wavelength of light they transmit. When E. coli 0157:H7 toxins bind to their synthetic membrane surface, the backbone chain of PDA reorganizes. The sensor that was blue turns red. Says Stevens, "These sensors have been designed so that the presence of this strain of E. coli causes a color change, from blue to red. The greater the color change in the sensor, the higher the concentration of 0157:H7. The color change is instantaneous. We can make an inexpensive sensor that can be placed on a number of different materials such as plastic, paper, or glass. The cost of the sensor is so nominal that it could be part of a bottle cap or container lid. If you open the product and the sensor has turned from blue to red, then you have a contaminated food product." With the ability to instantly detect 0157:H7, health authorities would have a powerful new weapon to combat what has been a continuing series of outbreaks. These include more than 380 cases of food poisoning and 10 deaths in Scotland this month, all linked to tainted meat; more than 60 confirmed cases of infections linked to unpasteurized fruit juice in late October; 9,400 cases of food poisoning in Japan during the Summer of 1995; and illness involving sausage and hamburger meat contamination in the U.S. in 1993 and 1994. The 0157:H7 strain thrives in animal fecal material which is why it often shows up in meat. Pasteurization of milk and juices -- a simple treatment with heat -- can kill the organism as can thorough cooking of meats. Children and the elderly are particularly susceptible to infections. Symptoms include diarrhea and internal bleeding, and death can result.
More about E. coli and advances in its detection
AE Activity: E. Coli and the Human Environment
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BERKELEY, CA 
Science Updates Index
