To test the system's ability to identify Salmonella, researchers grew bacteria from rinses of contaminated chicken, spinach, and peanut butter on agar plates for about 16 hours.  The laser identified Salmonella with 95.9 percent accuracy. (Credit: Dan Iggers/Flickr)

Laser tags salmonella in less than a day

A new laser sensor identifies Salmonella bacteria grown from food samples in less than 24 hours, about three times faster than conventional methods.

“BARDOT allows us to detect Salmonella much earlier and more easily than current methods,” says Arun Bhunia, professor of food science at Purdue University, who collaborated with then-Purdue engineer Daniel Hirleman to create the machine. “This could ultimately help provide safer food to consumers.”

Salmonella is a major foodborne pathogen that causes salmonellosis, a type of food poisoning with symptoms of diarrhea, fever, and abdominal cramps. Salmonellosis can be fatal in young children, the elderly, and those with compromised immune systems.

The US Food and Drug Administration has a zero-tolerance policy for Salmonella in food products. If the bacteria is detected, the resulting product recalls can lead to significant financial loss and possible charges of criminal liability for the companies involved.

BARDOT, short for “bacterial rapid detection using optical scatter technology,”  identifies bacteria colonies by using light to illuminate their natural characteristics, preserving the colonies for later study. The machine can be operated with minimal training and used in locations with limited resources, Bhunia says.

Bardot uses a red diode laser to scan bacteria colonies on an agar plate. When the light penetrates a colony, it produces a scatter pattern, a unique arrangement of rings and spokes that resembles the iris of an eye. The pattern is matched against a library of images to identify the type of bacteria.

Detects other bacteria, too

To test the system’s ability to identify Salmonella, researchers grew bacteria from rinses of contaminated chicken, spinach, and peanut butter on agar plates for about 16 hours. After the plates were covered with tiny spherical colonies of bacteria, they placed each plate inside Bardot—about the size of a large microwave oven—and scanned the colonies.

Salmonella bacteria was identified with an accuracy of 95.9 percent. Bardot also individually distinguished eight of the most prevalent Salmonella serovars—distinct variations within a species of bacteria. Identifying a particular serovar helps trace bacteria to the original source of contamination.

The system could be an effective preliminary screening tool, especially for food processors testing a large number of samples, says Atul Singh, postdoctoral research associate and first author of the study, published in mBio.

“Bardot screens quickly and inexpensively,” he says. “If you get a positive result for Salmonella, you can do a follow-up test. This can help food processors make more informed decisions.”

While many tools can only detect a single kind of bacteria, the new system picks out multiple types of disease-causing bacteria on a plate with a single scan, Bhunia says. In addition to Salmonella, it can identify E. coli, Vibrio, Listeria, Bacillus, and many more foodborne pathogens.

“That’s the beauty of this system,” Bhunia says. “It’s so versatile. It can find organisms that you didn’t even think about.”

Researchers from the Indiana State Department of Health also collaborated on the study, which was funded by the US Department of Agriculture, the National Institute of Allergy and Infectious Diseases, and the Center for Food Safety Engineering at Purdue.

Source: Purdue University

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