On a hot summer day, nothing spells refreshment quite like a slice of juicy, orange cantaloupe. But in summer 2011, cantaloupes reached plates with an unwanted addition: listeria. In the deadliest foodborne illness outbreak since 1925, cantaloupes contaminated with this bacterium killed 33 people.
Unfortunately, cantaloupes weren't the end of the story. A year later, listeria tainted another well-loved American staple: cheese. This time the bacteria killed four people. If the contamination had been detected before the food arrived on plates, these deaths could have been prevented.
A few months from now, a Boston-based start-up company will market a test kit that will do just that: detect this deadly bacterium in the processing plant, before it reaches the grocery store. They've used the tools of synthetic biology to create this novel, rapid test for Listeria contamination.
Scheduled for launch in July, the test developed by Sample6 Technologies provides results in three to four hours, compared to 16 and 48 hours for current assays for bacterial contamination.
The lag time built into existing tests forces companies that deal in perishable foods to make a tough choice between waiting for results or shipping potentially unsafe food.
"The faster you can get results, the closer to real time, the better off you are," said Will Daniels, senior vice president of Earthbound Farms. His company grows and packages organic salads and other produce. Daniels said Earthbound Farms is currently working with Sample6 to employ the more rapid test.
"It means that you could actually be testing while you're producing products and have the results before you ship it out. That's huge."
According to Daniels, Earthbound Farms currently tests for E.coli and Salmonella contamination using a polymerase chain reaction (PCR) test that takes 12 to 16 hours to generate results. The company doesn't use the test for listeria, however, because this bacterium takes close to 24 hours to detect.
Sample6 co-founders Mike Koeris and Timothy Lu, both synthetic biologists, hope the test will allow food processors to get the jump on bacterial contamination. Like the slower PCR test, Sample6's method detects bacteria in the environment of a processing facility, such as on machine surfaces.
"Testing the finished product is nice, but it's kind of too late because then, if you find it (contamination), you've got to throw away the food," said Koeris, who is Sample6's president and chief operating officer.
"It's much better if you test the process as it is working."
Sample6's test takes advantage of a bacteriophage specifically equipped to hone in on and infect listeria, as opposed to any other organism. Company scientists have engineered the bacteriophage so that it forces infected listeria to generate luciferase, the same enzyme that makes fireflies glow in the dark. "You put these phages on (a sample), and the phages will specifically recognize certain (bacterial) cells," Lu said.
"Only when those (bacterial) cells are present does the sample basically light up."
If a huge number of listeria are present, the light can even be seen by the naked eye. But food safety, of course, depends on the capacity to detect even a few pathogenic organisms. The Sample6 test kit includes a device about the size of a toaster oven that can detect light emitted by even a few listeria in a sample.
A worker can take a sample by first rubbing a sponge over a piece of processing equipment, such as conveyor belt, and then putting the sponge into the detector. If listeria organisms are present they'll light up.
The test package also includes a cloud-based software application for tracking when and where various locations have been sampled.
Food processors are the initial target market for Sample6's test kit, such as those who wash and package freshly harvested lettuce for retail sale. Twelve international food companies will begin using the system in July. It won't be generally available until January 2014.
"Fundamentally, the food industry wants to make sure the food they sell is safe," Koeris said. "Nobody wants to sell food that makes you sick."
Photo by Julianne Wyrick