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1. To establish a GFP-labeled L. monocytogenes and E. coli O157:H7 system.<P>
2. To determine the degree of E. coli O157:H7 cross-contamination of raw beef from a
contaminated meat grinder during grinding.<P>
3. To determine the degree of L. monocytogenes cross-contamination of RTE beef from a
contaminated meat slicer during slicing.<P>
4. To assess the degree of transfer of E. coli O157:H7 and L. monocytogenes from contaminated
stainless steel surfaces following cleaning and sanitizing.
Findings: Contamination from equipment is one way in which pathogens such as Listeria monocytogenes and Escherichia coli O157:H7 can gain entry into beef products. Discerning the rate of transfer of these pathogens from equipment to beef is challenging due to the difficulty in culturing these pathogens on selective media. The use of the green fluorescent (GFP) gene as a marker was shown in this study to be an effective way of monitoring the E. coli O157:H7 contamination of beef from contaminated equipment. Although we were unsuccessful at constructing a GFP-labeled L. monocytogenes, results using a wild type variant of the pathogen still showed the ability of transfer of this organism from contaminated slicer to roast beef during slicing for up to 40 minutes. The rate of decline of E. coli O157:H7 transferred from a contaminated meat grinder was slower than that for L. monocytogenes on a meat slicer. However, this may be attributed to differences in structural components of the meat grinder and slicer. The results of this study demonstrate the importance of cleaning and sanitization of beef processing equipment and confirms the importance of disassembling, cleaning and sanitization of equipment before, during and after processing. The use of the GFP gene as a marker to monitor the cross-contamination pattern in this study indicates the usefulness of such a system in these types of studies.