Foodborne illness is certainly less common in the U.S. than in many regions of the world, but it is far from rare. At least 159 people contracted E. coli at a fair in New York last month, and a recent report from the Centers for Disease Control estimates that each year tainted food causes 325,000 hospitalizations, 5,000 deaths and 76 million more-than-upset stomachs. The good news is that scientists are devising ever faster, cheaper ways to detect the organisms responsible for such infections. Electrochemical sensors are in the works and ones based on the polymerase chain reaction (PCR), although time-intensive, have proven extremely sensitive.
To this arsenal, researchers in Georgia have added a new weapon: their biosensor, unveiled on September 28, uses optics, immunoassays and other chemical tests to ferret out astonishingly small amounts of 12 different bacterial species within less than two hours.
Image: Georgia Institute of Technology
The sensor--developed over the course of four years by Georgia Tech biology professor Paul Edmonds, Nile Hartman of Georgia Tech Research Institute's Opto-Electronic Technologies Branch and Robert E. Brackett of the University of Georgia's Center for Food Safety and Quality Enhancement--is scheduled to begin field testing in November at Gold Kist, a food processing company based in Atlanta. "We will split a sample for testing with both of the technologies [the biosensor and the company's standard lab tests]," Hartman explains. "For every 1,000 tests we do, we will look for the variation between results of the two methods."
The biosensor promises to have several advantages over standard testing for bacterial pathogens, which is required by state and federal regulators for E. coli and Salmonella, although there are no standards for concentrations. Perhaps most significant, it needs less time to produce results. Current laboratory procedures can take up to 72 hours--delays that force companies to store meats in warehouses for longer periods, where they run a greater chance of being contaminated in the first place. "The biosensor will help in overall quality control in food processing plants," Edmonds notes. In addition, the biosensor--at roughly $1,000 to $5,000--costs less than the necessary lab equipment, estimated at $12,000 to $20,000. And it is 1,000 times more sensitive, detecting as few as 500 bacterial cells per milliliter of food.
Image: Georgia Institute of Technology
Although the device can identify 12 bacterial species, during field testing the researchers are focusing on six that most often appear in meat: Salmonella, Listeria monocytogenes, Yersenia enterocolitica, E. coli 0157:H7, generic E. coli and Campylobacter jejuni, now the most common cause of food poisoning. To find these organisms, the sensor uses integrated optic interferometric sensor technology, patented by Hartman and the Georgia Tech Research Corporation. Its waveguide is bound to antibodies that recognize proteins called antigens, which are distinct for different bacteria. When a bacterial antigen, coupled with urease enzymes, reacts with the antigens and urea is added, it produces gaseous ammonia; the gas, in turn, alters the sensor's optical properties and transmitted laser light, which indicates the concentration of the pathogen.
"If pathogens are found with the biosensor, then food processors can make decisions more quickly about applying treatments, such as antiseptics," Edmonds says. "Or they might divert those products to cooking operations, which would kill the pathogens. And companies could modify their sanitation plans."
Before commercializing the biosensor, though, the researchers have planned to do some serious fine-tuning. First they would like to boost the detector's sensitivity to 100 cells per milliliter, a level rivalling other devices under development. And they would like to broaden the sensor's range beyond meat pathogens to those found in poultry, seafood and dairy. "Also, we would like to use the biosensor to address other food safety issues, such as those associated with insecticides, pesticides and growth hormones," Hartman adds. If only they could get it to make toast.