Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 31, 2002
Publication Date: December 8, 2002
Citation: Tamplin, M.L., Marmer, B.S. 2002. Models of the behavior of e. coli 0157:h7 in raw ground beef and simulated gastric fluid. Society for Risk Analysis. Abstract # W144. Technical Abstract: Epidemiological reports show that ground beef is an important vehicle in transmitting Escherichia coli O157:H7 to humans. Risk assessments of E. coli O157:H7 have identified data gaps which can be reduced, in part, through the development of models that describe growth parameters, interstrain variation, and the temperature growth boundaries of E. coli O157:H7 in ground beef. Furthermore, the uncertainty in E. coli O157:H7 dose-response models can be reduced by describing the effects of gastric fluid on the survival of E. coli O157:H7 in cooked ground beef. In the present study, a model was produced for the growth of E. coli O157:H7 in a raw sterile ground beef matrix, including estimates of strain variation and the upper and lower temperature growth boundaries. Interestingly, no lag phase was observed at temperatures of less than or equal to 10°C, whereas at higher temperatures both lag phase duration and exponential growth rates decreased and increased, respectively. In addition, certain E. coli O157:H7 strains grew in ground beef`at temperatures lower than 9°C, whereas no growth was observed in brain-heart infusion bacteriological broth at 8°C or below. These observations also emphasize the potential uncertainties introduced in exposure assessment when bacteriological broth-based data are extrapolated to food matrices. Experiments of the fate of E. coli O157:H7 in cooked ground beef suspended in simulated gastric fluid (SGF) at ratios of 1:1, 1:10 and 1:100 demonstrated that the rate of inactivation decreased as the ratio increased, and that the rate of inactivation decreased with increasing concentrations of a commercial antacid. The slopes of the linear regression lines for SGF treatment versus survival rate were similar at 1:1 and 1:10 ratios, however the bactericidal effect was more than ten times greater at the 1:100 ratio. Comparisons of the inactivation rates of Shigella spp. and E. coli O157:H7 in SGF showed that the former is markedly more sensitive to SGF.