Method Developed to Detect Live E. coli in Ground Beef

September 7, 2009 07:00 PM

By Robert E. Thomas, University of Missouri

E. coli Facts

According to the national Centers for Disease Control and Prevention, about 70,000 people in the U.S. become ill each year from infection with Escherichia coli O157:H7. This bacterium colonizes the intestinal tract of cattle and can contaminate beef products during slaughter and processing.

University of Missouri food scientists have come up with a new method to detect live E. coli cells in ground beef.

The MU researchers developed a two-step method that can distinguish between dead and living E. coli cells. Dead cells won't make you sick, but as few as 10 live cells can inflict a severe intestinal illness, said Azlin Mustapha, associate professor of food science in the MU College of Agriculture, Food and Natural Resources.

"This is the first such research using these methods in testing beef,” she said. Mustapha and colleagues reported on the research in the Journal of Applied Microbiology.

The research employs a technique called a real-time polymerase chain reaction (PCR). This is a quick, reliable method for detecting and identifying pathogens in food. PCR, however, can't differentiate viable from dead microbial cells. The presence of dead pathogenic cells may result in false-positive findings, which could lead to unnecessary product recalls, Mustapha said.

To prevent this, researchers stain samples with a dye called ethidium bromide monoazide. EMA can't penetrate live cells, but it can enter dead cells, where it binds to DNA molecules, making them insoluble and therefore invisible to PCR tests.

The researchers have successfully tested the technique on ground beef, chicken and eggs, Mustapha said.

Testing takes about 12 hours, as opposed to older methods, which require up to two days for results.



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