New Sensor Provides First Instant Test for Toxic E. Coli Organism
|By Jeffery Kahn, JBKahn@lbl.gov
December 10, 1996
BERKELEY, CA -- Researchers have developed a sensor that, for the first time, can instantly detect the presence of toxic E. coli bacteria. Contamination by this bacteria is responsible for recent illnesses and deaths in the United States involving fruit drinks and fast-food hamburgers, a massive outburst of food poisoning in Japan, and a current outbreak in Scotland that is linked to 10 deaths.
Raymond Stevens, a chemist
at the Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab), says the sensors his team have developed are capable of providing an extremely inexpensive, on-the-spot litmus test for E. coli strain 0157:H7. First identified as a threat to humans in 1982, 0157:H7 is the virulent strain of E. coli responsible for these outbreaks.
Illustration courtesy of Chemistry & Biology magazine
Says Stevens, "These sensors have been designed so that the presence of the toxin produced by 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 toxin. The color change is instantaneous."
Up until now, no technology existed that would allow either food companies, health inspectors, or consumers to determine immediately whether E. coli 0157:H7 is present. Currently, the best detection method requires the taking of a sample which must be cultured for 24 hours. Only then can technicians ascertain whether the bacteria are present (with the use of a variety of tools ranging from microscopes to dyes.) Another detection technique, now under development, relies on polymerase chain reaction technology to multiply the amount of bacterial DNA present in a sample to detectable levels. Several hours must pass, however, before results can be obtained.
The instant analysis provided by Berkeley Lab's new sensors has obvious advantages as a public health tool. Dangerous pathogens can be detected before a food product has been shipped to the store. Another advantage is cost.
Says Stevens, "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."
As for the maturity of the technology, a number of steps must occur before these sensors can be used commercially. The technology must be licensed to a private company. And then, it must be refined and adapted for mass manufacture and sale.
Stevens, who is also an assistant professor of chemistry at the University of California at Berkeley, developed the sensors in concert with Berkeley postdoc Quan Cheng. The device is a modification of one originally described in the journal Science by former Lab scientist Mark Bednarski and Lab materials scientist Deborah Charych. All are current or former members of Berkeley Lab's Biomolecular Materials Program in its Center for Advanced Materials. The center does basic research relevant to both the needs of industry and the Department of Energy.
Technically, the working part of the sensor consists of multiple copies of a single molecule which is fabricated into a thin film. This molecule has a two-part composite structure. The surface of the molecule -- developed by Stevens and Cheng -- binds the bacteria toxin. The backbone underlying this surface is the color-changing signaling system described by Bednarski and Charych.
The Biomolecular Materials Program focuses on adapting nature's biological systems to problems outside the living organism. In this case says Stevens, "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."
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.
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 illnesses 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. The bacteria strain is a potent health threat. Undoubtedly, numerous unreported outbreaks of E. coli related disease have occurred. Children and the elderly are particularly susceptible to infections. Symptoms include diarrhea and internal bleeding, and death can result.
Berkeley Lab has several patents pending on its sensors, which now are available for licensing to private industry. Firms interested in information about licensing should contact Viviana Wolinsky in the Lab's Technology Transfer Department. Wolinsky can be reached at 510-486-6467 or via e-mail at email@example.com.
Berkeley Lab conducts unclassified scientific research for the U.S. Department of Energy. It is located in Berkeley, California and is managed by the University of California.