Apr. 27, 2000 FAYETTEVILLE, Ark. — Researchers at the University of Arkansas have found a way to detect as few as 5,000 Salmonella bacteria from a chicken carcass sample in two hours. Their detection method may one day lead to faster, more sensitive and more comprehensive biological sensors in the food industry.
Yanbin Li, and Michael Slavik, professors of poultry science, and David Paul, chemistry, will publish their findings in an upcoming issue of the Journal of Food Protection.
The Centers for Disease Control and Prevention in Atlanta estimate that every year, 800,000 to 2 million people experience the fever, cramps and diarrhea that accompany a S. typhimurium infection. Most of those afflicted contract the disease through contaminated food or water.
While such food poisoning can be prevented by hand washing and thoroughly cooking meat, the University of Arkansas researchers are trying to build a detector that would find Salmonella on the spot — before the meat ever leaves the packing plant.
"After two hours, the sampled food may be in the factory," Slavik said. This could save consumers from buying contaminated foods and manufacturers from making costly recalls.
Li , Slavik and Paul are pooling their expertise in bacteriology, food processing and micro sensors to create an on-site biosensor that can detect Salmonella.
"Biosensors are the better way to get to on-line, real-time detection of bacterial contamination in processing plants," Li said.
The current culture method of Salmonella detection requires swabbing the meat and growing the bacteria for three days, an unrealistic practice for a processing plant that may process and send out millions of chickens each day.
To speed up the detection process, the researchers have created a raw "chicken soup" by shaking a chicken carcass in a plastic bag with a buffer. They pour the soupy buffer mixture into a test tube filled with small magnetic beads coated with antibodies that bind a specific Salmonella strain. The scientists wash the mixture with another buffer, using a magnet to pull the beads over to one side with the Salmonella bound to the antibody.
Then they add an enzyme which attaches to the S. typhimurium bacteria. They wash the excess enzyme off, again using the magnetic beads to keep the antibody-bacteria-enzyme sandwich intact.
The scientists add phenyl phosphate to the mixture. The enzyme attached to the bacteria chops up the phenyl phosphate to create phenol, which can be detected by an electrode. The reaction takes place in less than an hour, and the amount of phenol produced is directly proportional to the amount of bacteria in the sample.
Using this method, as few as 5,000 bacteria can be detected in two hours, with an electrode the size of a pen.
The scientists continue to look at ways to speed up the detection process and detect fewer and fewer bacteria, Li said. They will focus on microbial, engineering and chemical methods to speed up the reaction time. They will also try to reduce non-specific binding to the antibodies, which will increase the test’s accuracy.
Although better detection methods can help reduce the incidence of Salmonella in raw animal products, it won’t eliminate the problem of food-borne illness. A detector could never guarantee that the entire volume of meat processed in the average processing plant is Salmonella free, Slavik said, because only a small portion of the meat processed on a given day can be tested. Salmonella contamination can also occur after the meat has left the processing plant — from unwashed hands and cross-contamination while preparing foods.
"The only thing we can do is try to make sure there are no bacteria on the tested carcass when it leaves the plant," Paul said.
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