Examine how L. monocytogenes moves from processing equipment to deli meats.

Contamination by L. monocytogenes of ready-to-eat luncheon meat has resulted in a number of product recalls. Listeriae appear to be able to survive well in processing facilities, including on meat-slicing equipment.

The purpose of research at the University of Georgia was to determine the dynamics of cross-contamination of L. monocytogenes from a commercial slicer onto sliced meal products. Three types of deli meats--oven-roasted turkey, salami and bologna--were tested. Of these, salami had the lowest moisture content and pH, and the highest salt content. Bologna and turkey had similar pH values and moisture contents, but bologna contained growth inhibitors to L. monocytogenes.

Researchers inoculated a five-strain mixture of L. monocytogenes at 103 CFUs onto the slicer blade. Meats were sliced and packaged. Five meat slices were packed per package, and 200 packages were vacuum-sealed, held at 4 C and analyzed on days 1 and 30 after the meat was sliced. Two sample sizes, 25 grams and an entire package of meat, were assayed for L. monocytogenes, according to the USDA protocol.

Scientists detected L. monocytogenes in 1%, 5% and greater than 10% of bologna, salami and turkey slices, respectively. A higher percentage of turkey meat samples (27%) was positive when the entire sample, rather than a 25-gram sample (13%), was assayed. But similar percentages of bologna and salami samples were positive for L. monocytogenes for both sample sizes. The number of positive samples increased during storage of turkey meat but decreased for salami and bologna slices.

L. monocytogenes was detected on more sections of the slicing equipment after salami was sliced than either the turkey or bologna. These results indicate that the pathogen can be transferred from a highly contaminated slicer onto meats. It can survive or grow better on oven-roasted turkey than on salami or bologna containing preservatives. Analyzing larger amounts of turkey meat, but not salami or bologna slices, enabled the researchers to detect higher numbers of samples containing L. monocytogenes.

Further information. Michael Doyle, Center for Food Safety, University of Georgia, Griffin Campus, Melton Building, Griffin, GA 30223; phone: [phone]; fax: [phone]; email: [e-mail].