Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 29, 2005
Publication Date: April 15, 2005
Citation: Tamplin, M.L., Paoli, G., Phillips, J.G., Marmer, B.S. 2005. Improving secondary models for the behavior of Escherichia coli 0157:H7 in raw sterile ground beef stored at 5 deg to 46 deg c. International Journal of Food Microbiology. V. 100. P. 335-344. Interpretive Summary: Escherichia coli O157:H7 can contaminate raw ground beef and cause serious human foodborne illness. Consequently, food industries require tools to assist in evaluating different food processing strategies to control levels of E. coli O157:H7 in ground beef products. Presently, predictive models are used by the food industries to estimate the growth, survival and inactivation of bacterial pathogens, and have been useful in designing food safety systems, such as HACCP programs. Such models are also used by risk assessors to measure the impact of foodborne pathogens on human health. However, the utility of predictive models depends on their validated performance under specific food processing conditions. In the present study, predictive models were produced that provide more accurate estimations of E. coli O157:H7 behavior in irradiated raw ground beef, in comparison with previous models developed in microbiological broth. The models were produced by measuring the growth and inactivation of multiple E. coli O157:H7 strains stored in ground beef at a temperature range of 5 to 46 C. Growth occurred from 6 to 45 C. Lag phases in growth were observed at all test temperatures, except at 8 or 10°C. The growth rate of E. coli O157:H7 increased from 6 to 42°C. The new models improve the accuracy of the predictions for E. coli O157:H7 lag phase and growth rate when compared to the performance of an existing USDA Pathogen Modeling Program (PMP) E. coli O157:H7 broth-based model, especially for temperatures below 20 C. The new ground beef models will be incorporated into the PMP and the data sets from these studies will be incorporated into a relational database, ComBase, scheduled for release on the Internet in 2003. These resources will assist ground beef operations and risk managers in designing better strategies to reduce the risk of E. coli O157:H7 disease associated with ground beef products.
Technical Abstract: Escherichia coli O157:H7 can contaminate raw ground beef and cause serious human foodborne illness. Previous reports describe the behavior of E. coli O157:H7 in ground beef under different storage conditions, however models are lacking for the pathogen's behavior in raw ground beef stored over a broad range of temperatures. Using sterile irradiated raw ground beef, the behavioral kinetics of 10 individual E. coli O157:H7 strains and/or a 5- or 10-strain cocktail were measured at storage temperatures from 5 to 46 C. Growth occurred from 6 to 45 C but not at 5 or 46°C. Although lag phase duration (LPD) increased from 45 to 10.5 C, no lag phase was observed at 8 or 10°C. The specific growth rate (SGR) increased from 6 to 42°C, then declined up to 45°C. In contrast to these profiles, the maximum population density (MPD) displayed a moderate decline from approximately 9.7 to 8.2 log cfu/g over the experimental temperature range. A measurement of the performance of the USDA Pathogen Modeling Program in ground beef from 10 to 42 C for the parameters of SGR, LPD, and MPD showed model bias (Bf) factors of 1.21, 2.70, 1.00 and model accuracy factors (Af) of 1.26, 2.87, 1.03, respectively. In general, greater bias was observed at temperatures below 20 C. The performance of the new secondary models from 10 to 42 C for SGR, LPD and MPD showed Bf of 1.03, 1.03, 1.00, and Af of 1.14, 1.41, 1.02 respectively. The improved models can provide more accurate estimates of the behavior of E. coli O157:H7 in raw ground beef.