Biosensors detect Salmonella.

Researchers at the University of Arkansas (Center of Excellence in Poultry Science, O-411 Poultry Science Building, Fayetteville, AR 72701) are developing a sensor that detects as few as 5000 Salmonella bacteria from a chicken carcass sample in 2 hr. Their innovation may lead to faster, more sensitive and more comprehensive biological sensors in the food industry.

While such food poisoning can be prevented by hand washing and thoroughly cooking meat, the University of Arkansas researchers are building a biosensor that would find Salmonella on the spot-before the meat ever leaves the packing plant. This could save consumers from buying contaminated foods and manufacturers from making costly recalls.

The investigators are pooling their expertise in bacteriology, food processing and sensor technology to create an electrochemical biosensor for use on the factory floor to detect Salmonella in products as they come off a production line. Biosensors are the better way to get to real-time detection of bacterial contamination in processing plants. The current culture method of Salmonella detection requires swabbing meat and growing the bacteria for three days, an unrealistic practice for a plant that may process and send out thousands of product each day.

The researchers created a raw chicken soup by shaking a chicken carcass in a plastic bag with a buffer. They poured the soupy buffer mixture into a test tube filled with small magnetic beads coated with antibodies that bind a specific Salmonella strain. The scientists washed 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 added an enzyme that attaches to the S. typhimurium bacteria. They washed the excess enzyme off, again using the magnetic beads to keep the antibody-bacteria-enzyme sandwich intact. The scientists added phenyl phosphate to the mixture. The enzyme attached to the bacteria changed the phenyl phosphate to phenol, which was detected by an electrode. The reaction took place in less than an hour, and the amount of phenol produced was directly proportional to the amount of bacteria in the sample.

Using this technique, as few as 5000 bacteria can be detected in 2 hr with an electrode the size of a pen. The scientists are trying to speed up the entire detection process-possibly to 1 hr-and make it possible to detect fewer bacteria, possibly 100 cells. 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 foodborne illness. A sensor can never guarantee that the entire volume of meat processed in a facility is free of bacteria 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 that may occur while preparing foods.

Officials at the U.S. Centers for Disease Control and Prevention estimate that every year 800,000 to 2 million people experience the fever, cramps and diarrhea that accompany S. typhimurium infection. Most of those afflicted contract the disease through contaminated food or water.

Further information. Yanbin Li; phone: [phone]; fax: [phone]; email: [e-mail].