Project Summary

Real-time Monitoring of Cross-contamination of Listeria monocytogenes between Equipment and Ready-to-Eat Meat Products via a GFP Reporter

Principle Investigator(s):
Azlin Mustapha
University of Missouri
Completion Date:
May 2007



Listeria monocytogenes is a ubiquitous bacterium commonly found on raw meat and poultry products and has been associated with a number of foodborne illness outbreaks and food product recalls (CDC 1999; USDA-FSIS 2003a). This organism possesses a relatively high resistance to heat and can grow at refrigeration temperatures as low as 2°C and under low oxygen tension, such as that found in vacuum-packaged ready-to-eat (RTE) products (Samelis and others 2002). L. monocytogenes is given a zero-tolerance status in RTE meat and poultry products because of the high mortality rate associated with listeriosis (Mead and others 1999). Although the cooking processes currently applied by the meat industry generally meet USDA Food Safety and Inspection Service (FSIS) requirements, the processing steps after cooking such as peeling, sorting, loading, slicing, packaging, and so forth, are potential sources of recontamination. An FSIS survey published in 2001 showed that 1% to 10% of retail RTE products were contaminated with L. monocytogenes (Levine and others 2001). L. monocytogenes is currently the most concerned pathogen of post-cook contaminants among RTE meat and poultry products.

The CDC estimates the annual cost of illness due to Escherichia coli O157:H7 infections acquired from food or other sources as $405 million (Frenzen et al., 2005). Because of the high cost of illness due to E. coli O157: H7 infections, the federal government has implemented mandatory hazard analysis and critical control point (HACCP) programs and improved pre- and post-harvest processes to lower the contamination levels of meat products with this pathogen in meat and poultry plants and the juice industry (Frenzen, 2005). Most outbreaks of E. coli O157:H7 have been the associated with foods of bovine origin. In cases involving non-bovine foods, cross-contamination by beef or contamination with bovine feces during processing has often been suspected. It is believed that E. coli O157:H7 contamination of foods occurs from the intestinal tract of healthy cattle during slaughter and processing (Wells et al., 1991; Wang et al., 1996). Cross-contamination in abattoirs (Bouvet et al., 2001; Warriner et al., 2002) and other food processing plants (Beuchat and Ryu, 1997; Warriner et al., 2002) have been reported to be responsible for several outbreaks of E. coli O157:H7. E. coli O157:H7 is known to produce extracellular polymeric substances (EPS) and form biofilms on food processing surfaces (Junkins and Doyle, 1992; Dewanti and Wong, 1995; Ryu et al., 2004). Microorganisms are known to be more resistant to removal from foods and food contact surfaces in processing plants and to inactivation by sanitizers when contained in a biofilm than when dispersed in a liquid medium (Kumar and Anand, 1998; Carpentier and Cerf, 1992).

The stated objectives for this work were: 

  • To establish a GFP-labeled L. monocytogenes and E. coli O157:H7 system. 
  • To determine the degree of E. coli O157:H7 cross-contamination of raw beef from a contaminated meat grinder during grinding.
  • To determine the degree of L. monocytogenes cross-contamination of RTE beef from a contaminated meat slicer during slicing.
  • To assess the degree of transfer of E. coli O157:H7 and L. monocytogenes from contaminated stainless-steel surfaces following cleaning and sanitizing.

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