P2-08 Thermal Tolerance of O157 and non-O157 Shiga Toxigenic Strains of Escherichia coli, Salmonella spp. and Potential Pathogen Surrogates in Frankfurter Batter and Ground Beef of Varying Fat Levels

Tuesday, August 5, 2014
Exhibit Hall D (Indiana Convention Center)
Akhila Vasan, University of Wisconsin-Madison, Madison, WI
Renae Geier, University of Wisconsin-Madison, Madison, WI
Steve Ingham, Wisconsin Department of Agriculture, Madison, WI
Barbara Ingham, University of Wisconsin-Madison, Madison, WI
Introduction: Non-O157 Shiga toxigenic Escherichia coli (STEC) serogroups most commonly associated with illness are O26, O45, O103, O111, O121, and O145.

Purpose: Thermal tolerance (D55°C) of three strains of six non-O157 STEC serogroups was compared with five O157:H7 STEC strains in 7% fat beef. D55°C was determined for > 1 heat-tolerant STEC strain per serogroup in 15 and 27% fat beef. D55°C of single-pathogen cocktails of O157- and non-O157 STEC, Salmonella spp., and potential pathogen surrogates, Pediococcus acidilactici and Staphyloccous carnosus, was determined in 7, 15, and 27% fat beef and in frankfurter batter.

Methods: Samples (25 g) were heated for up to 120 min at 55°C, rapidly cooled, stomached, and plated. Log CFU/g of survivors was plotted versus time and D55°Ccalculated.

Results: There was significant difference in D55°C across all STEC strains in 7% fat beef (P < 0.05), but none of the non-O157 STEC strains were more heat tolerant than the range for O157 STEC. There were significant differences in D55°C within serogroups O45, O145, and O157 (P < 0.05). D55°C-values for non-O157 STEC strains heated in 15 and 27% fat beef were < the range for serogroup O157 (P ≥ 0.05).  D55˚C of pathogen cocktails was not different in 7, 15, and 27% fat beef (P > 0.05). D55°C of Salmonella spp. in frankfurter batter was significantly less than for O157 and non-O157 STEC (P < 0.05). Thermal tolerance of pathogens in ground beef (7, 15, or 27% fat) and frankfurter batter was significantly less than for potential surrogates (P < 0.05).

Significance: Results suggest that thermal-processing interventions validated against E. coli O157:H7 have adequate lethality against non-O157 STEC, that thermal processing interventions which target Salmonella destruction may not be adequate against STEC in all situations, and the use of pathogen surrogates P. acidilactici and S. carnosus to validate thermal processing interventions in ground beef and frankfurter batter would of limited utility to processors.