Firefly gene sheds light
on harmful food bacteria
by Anne Douglas
Office of Research
For meat companies that must contend with food bacteria such as salmonella and E. coli, there may be light at the end of the tunnel . . . and it's coming from fireflies.
Few processing companies have been able to test meats or other foods for harmful bacteria because the tests take too long. But that's all changing thanks to Prof. Mansel Griffiths, chair of the Department of Food Science. He's found that the gene that causes fireflies and other luminescent organisms to glow - the lux gene - could help detect the presence of deadly bacteria in meat and other foods.
"It's widely recognized by meat companies and regulatory agencies that rapid test methods for dangerous bacteria in foods are necessary," says Griffiths. "The lux gene system may be exactly what's needed. It can be inexpensive and easy to work with and can detect bacteria in three to six hours."
Thousands of serious illnesses and deaths occur in Canada each year from bacteria in food. As a result, Canadian and U.S. regulatory agencies have identified dangerous bacteria in food as a top priority. But to test meat for bacteria before the lux gene came along, scientists had to take a sample of meat, put it in a growth medium and wait for a colony of bacteria to form. Then they could identify the bacteria based on the physical characteristics of the colony. This method could take up to three days, by which time the meat should have been in the grocery store.
The main selling point of Griffiths's system is that it's fast. Here's how it works:
This lux gene system could be used for more than food-safety testing, says Griffiths. It could be used to determine the points in food processing that are critical to stopping contamination or growth of poisonous food bacteria. The lux gene may also be used to test food after it's undergone processing to verify the effectiveness of the processing methods.
- Lux genes are removed from a glowing organism and installed in a virus, called a bacteriophage, which preys on a specific type of bacteria (in this case, food bacteria).
- The bacteriophage is mixed with the meat sample and, if it finds its bacterial prey, transfers the lux gene to that bacterium.
- The infected bacterium copies the gene and expresses it, meaning it begins to glow.
- The sample is put into a charge-coupled device camera, which amplifies the light from the lux gene in the food bacteria and transmits it as an image to a computer monitor. The brighter the image, the more harmful bacteria are present.
- If the meat is found to have harmful bacteria in it, the processing plant will divert it to a different product, such as canned meat, which receives enough processing to kill the bacteria.
Griffiths's bacteria-detection system can detect the four most dangerous food illnesses: salmonella, commonly found in poultry; E coli 0157, also known as hamburger disease; Staphylococcus aurus, a common type of food poisoning; and Listeria monocytogenes, which can result in severe blood poisoning and meningitis.
Griffiths says one of his tests can detect several types of deadly bacteria at the same time by putting different lux genes with specific light properties in various types of bacteriophages, which each infect one type of bacteria.
Other researchers who have contributed significantly to this work are research associate Sabah Jassim, postdoctoral fellows Maria Hernandez and Jinru Chen and graduate student Franco Pagotto, all of the Department of Food Science, and Moscow State University chemist Luba Brovko.
This research was sponsored by the Natural Sciences and Engineering Research Council, Dairy Farmers of Ontario, Ontario Ministry of Agriculture, Food and Rural Affairs, Agriculture and Agri-Food Canada, Canadian Egg Marketing Agency and University Research Incentive Fund.
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