Food Safety
New way to detect live E. Coli in ground beef 11 Sep 2009
University of Missouri food scientists have come up with a new method to detect live E. coli cells in ground beef.
According to the American National Centers for Disease Control and Prevention, about 70,000 people in the US become ill each year from infection with Escherichia coli O157:H7. This bacterium colonises the intestinal tract of cattle and can contaminate beef products during slaughter and processing.
The U of M researchers developed a two-step method that can distinguish between dead and living E. coli cells. Dead cells won’t cause illness; however, as few as 10 live cells can inflict a severe intestinal illness, said College of Agriculture, Food and Natural Resources.
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.
According to Azlin Mustapha, associate professor of food science at U of M, to prevent false-positive findings, 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 report they have successfully tested the technique on ground beef, chicken and eggs. Testing takes about 12 hours, as opposed to older methods, which require up to two days for results.
The U of M researchers developed a two-step method that can distinguish between dead and living E. coli cells. Dead cells won’t cause illness; however, as few as 10 live cells can inflict a severe intestinal illness, said College of Agriculture, Food and Natural Resources.
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.
Real time PCR
Real time PCR is based on the polymerase chain reaction, which is used to amplify and simultaneously quantify a targeted DNA molecule. It enables both detection and quantification of a specific sequence in a DNA sample. The procedure follows the general principle of polymerase chain reaction; its key feature is that the amplified DNA is quantified as it accumulates in the reaction in real time after each amplification cycle.
According to Azlin Mustapha, associate professor of food science at U of M, to prevent false-positive findings, 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 report they have successfully tested the technique on ground beef, chicken and eggs. Testing takes about 12 hours, as opposed to older methods, which require up to two days for results.
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