New devices detect Salmonella, E. coli, other bacteria

provided by University of Rhode Island

ore than 75 million people per year become ill from food poisoning in the United States, 325,000 are hospitalized, and 5,000 of them die from pathogens like Salmonella and E. coli. But detection of these pathogens is getting easier, thanks to several new biosensors developed by researchers at the University of Rhode Island.

Ten years in development, the biosensors use fiber optic technology to quickly and accurately detect and quantify bacteria levels in meats, poultry and other foods.

"There are about 6,000 meat and poultry processing plants in the United States, and they all are required by law to test their products for food pathogens," said A. Garth Rand, professor emeritus of food science at URI. "Most of these plants don't have their own labs, so they've got to send their samples out to commercial labs. Instead of waiting several days to get results, they can use our biosensor and have results in an hour."

Rand teamed up with Stephen Letcher, professor of physics, and Christopher Brown, professor of chemistry, to establish the URI Fiber Optic & Biosensor Research Group to tackle the difficult problem of developing a fast and sensitive food pathogen sensor.

This research group is part of the University's Sensors and Surface Technology Partnership. The US Department of Agriculture has funded the research for the past eight years. "We are one of a very small number of research groups working on food safety biosensors," said Rand. "And our combination of disciplines is unique. The only way to solve this kind of problem is with an interdisciplinary approach."

Focusing first on detecting Salmonella, one of the most common food pathogens, the group developed several sensors that use vibrating quartz crystals or fiber optic probes along with Salmonella antibodies that bind the pathogen cells to the sensor. The latest version also uses microscopic magnetic beads called microspheres.

"The surface of the beads are covered with antibodies that collect the pathogen and are then labeled with a fluorescent dye," explained Rand. "Then the beads are magnetically focused in front of optical fibers and a laser signal reports the pathogen concentration."

The binding of the pathogen cells to the antibodies takes about 60 minutes, while the process of determining the pathogen concentration takes just 60-90 seconds.

Although the sensor needs further refinement before it is complete, the researchers are working with Pierson Scientific Associates of Andover, Mass., to develop portable prototypes of the device. The partnership was awarded a Small Business Technology Transfer grant from the National Science Foundation in 1998.

"While we've been primarily studying Salmonella, the system works for most other food pathogens, too," Rand said. "In fact, we believe it works even better for E. coli."

The URI researchers have also been working on biosensors for the US Army Natick Labs, which prepares Defense Department meals that are often stored for years in remote locations. The Army has funded Rand's research into developing sensors to detect pathogens in Army rations.

"They are especially concerned with detecting pathogens that grow in low-moisture dried foods," explained Rand. "They needed a quick way to see if pathogens are growing in the food they have stored around the world." For this project, Rand's team developed a membrane biosensor. When the membrane is coated with antibodies and enzymes, the bacteria gets caught on the membrane while the rest of the solution being tested passes through it. Next up for the URI researchers is the creation of a hand-held surface scanning system - similar to a supermarket checkout scanner that uses video to detect the pathogens, and another that detects pathogens in seafoods.

"These sensors will significantly enhance the safety of the food supply and protect human health," concluded Rand.