Live cells detect food-borne pathogens and toxins

Purdue University researchers have reported a new technology for potential biosafety and food safety applications that can simultaneously screen thousands of samples of food or water for several dangerous food-borne pathogens within a couple of hours.

The technique also can estimate the amount of microbes present and whether they pose an active health risk. This could help neutralize potential threats and improve food processing techniques, says Arun Bhunia, a professor of food science at Purdue University.

“For food safety and biosecurity purposes, you need a quick test—a first line of defense—to be able to tell if there is something pathogenic in the food or water,” Bhunia says.

The detection method employs live mammalian cells that release a measurable amount of a signaling chemical when harmed. According to Bhunia, optical equipment and computer software can then be used to analyze the chemical to estimate the amount of harmful microbes present, which is important because there is an effective dose or threshold that many toxins or pathogens need to pass before setting off a red flag for addressing the problem.

The technology can recognize very small amounts of Listeria monocytogenes, a bacterium that kills one in five people infected and is the leading cause of food-borne illness. It also recognizes several species of Bacillus, a non-fatal but common cause of food poisoning, says Pratik Banerjee, a Purdue researcher and first author of a study published in the February issue of the journal Laboratory Investigation detailing the technology. The study was funded by the U.S. Department of Agriculture and Purdue’s Center for Food Safety Engineering.

Purdue researcher Pratik Banerjee, at left, measures fluid as he and professor of food science Arun Bhunia work in the lab. Their technology uses common lab materials to quickly screen food and water samples for several food-borne pathogens and toxins. Photo by Tom Campbell/courtesy of Purdue Agricultural Communication.
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The cells are suspended in collagen gel and put into small wells within multi-well plates, which may allow them to be prepared in a central location and shipped to a processing location for on-site testing. This suspension of live mammalian cells within a collagen gel is unique, according to the researchers.

The technology tests for bacteria and toxins that attack cell membranes. For this reason, researchers used cells with high amounts of alkaline phosphatase, the signaling chemical released upon damage to the cell membrane. Researchers could conceivably employ other types of cells within this framework to detect additional types of pathogens.

Samples of food and water are added to biosensor wells before being incubated for 1 to 2 hours. To each well, a chemical is added that reacts with the biosensor’s alkaline phosphatase, yielding a yellow product quantified by a special camera and a computer. However, a precise calculation may be unnecessary sometimes.

“When a large amount of pathogen is present, you can literally see the color change taking place before your eyes,” Banerjee says.

According to the researchers, this technology can actively identify harmful pathogens but ignore those that are inactive, or harmless. Some comparable tests lack this ability and have a tendency to produce false alarms; the incubation period to grow out any living microbes is also rather long with such tests. The new technology also could help optimize processes to kill harmful microbes or deactivate toxins.

The cells currently only live between 4 to 6 days within the gel; Bhunia says this time span could be expanded to 2 weeks, the shelf life he deems necessary for commercial application.


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