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E. coli O157:H7 Duped by Built-in Food Safety Mechanism

By March 8, 2010

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The North American Summit on Food Safety starts tomorrow and I promised to tell the interesting story of how Dr. Rick Holley's laboratory is using applied food biotechnology to build safety into meat products. In a chain of events somewhat analogous to the activation of suicide genes in GMOs released to the environment during bioremediation, the Holley lab has found a way to set up E. coli O157:H7 to indirectly cause its own demise.

Mustard seed contains a natural anti-microbial compound called isothiocyanate, which is produced when the plant is attacked by bacteria or fungi. The precursor compounds to isothiocyanate, called glucosinolates, are stored in different cells of the plant than the enzyme myrosinase, which is required to cleave the glucose molecule and generate the anti-bacterial compound. When cells are damaged in the plant, the enzyme finds the substrate and the infection is stopped. The Holley lab has found that adding powdered mustard to sausages prevents contamination by bacteria. Mustard is a common spice and does not have to undergo regulatory testing as a food additive. The problem is that once the seed is powdered, the enzyme and glucosinolates are in contact and the meat will have a mustard flavor. To avoid this, the powder is heat-treated, inactivating the enzyme. The powder still has antimicrobial activity because the Holley lab has discovered that E. coli O157:H7 cells themselves produce myrosinase, probably because they detect the glucose ligand on the substrate and want to use it as an energy source. Unfortunately for them, the resulting side effect is production of the bactericidal isothiocyanate.

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