Muscle and fat exert different protective effects on bacteria.

E. coli O157:H7 is pathogenic and virulent. A resultant foodborne infection can cause hemolytic uremic syndrome, a disease primarily of infancy and early childhood. It is characterized by a triad of microangiopathic hemolytic anemia, thrombocytopenia and acute renal failure.

Currently, large quantities of meat go to waste because of its presence. The meat industry utilizes bacterial intervention techniques, including steam pasteurization and organic acid washes, to reduce the bacterial counts on carcasses. These interventions do not kill all bacteria, and instead may create an environment that allows pathogenic E. coli to thrive.

Scientists at Canada's University of Alberta transformed an isolate from a meat packing plant and a laboratory strain of E. coli to carry plasmids that produce fluorescent proteins (FPs)--red fluorescence proteins or green fluorescent proteins. The fluorescence intensities of these proteins are dependent on their ambient pH. Viable bacterial cells fluoresce brightly. Injured or dead cells fluoresce less when the pH is below 5.5.

Bacteria found below depths of 200 mm in meat products survive many current interventions. The researchers inoculated muscle and fat tissue cores of 4.9 [cm.sup.2] with E. coli and subjected them to steam and lactic acid treatments. The differences between strains and tissues after the treatments were not significant. However, steam treatments on fat tissue were significantly less effective in reducing bacterial numbers than the steam treatments on muscle tissue. Lactic acid contributed substantially to the overall bactericidal effect on fat tissue. But it had a minimal effect or no effect at all on muscle tissue.

This indicates that muscle and fat have different protective effects for bacteria against lactic acid and steam treatments. Because of this, some current meat industry intervention steps may fail to reduce microbial populations sufficiently to ensure that E. coli is not passed to the consumer on non-intact raw beef.

Further information. Dana Pierce, Department of Agricultural, Food and Nutritional Science, University of Alberta, Room 2-50, Agriculture/Forestry Centre, Edmonton, Alberta T6G 2P5, Canada; phone: 780-492-3634; fax: 780-492-4265; email: dana.pierce@ualberta.ca.

The USDA has a zero-tolerance policy for E. coli O157:H7 on non-intact beef.

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