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

Abstract

The non-O157 Shiga toxigenic Escherichia coli (STEC) serogroups most commonly associated with illness are O26, O45, O103, O111, O121, and O145. We compared the thermal tolerance (D55°C) of three or more strains of each of these six non-O157 STEC serogroups with five strains of O157:H7 STEC in 7% fat ground beef. D55°C was also determined for at least one heat-tolerant STEC strain per serogroup in 15 and 27% fat ground beef. D55°C of single-pathogen cocktails of O157 and non-O157 STEC, Salmonella, and potential pathogen surrogates, Pediococcus acidilactici and Staphylococcus carnosus, was determined in 7, 15, and 27% fat ground beef and in frankfurter batter. Samples (25 g) were heated for up to 120 min at 55°C, survivors were enumerated, and log CFU per gram was plotted versus time. There were significant differences in D55°C across all STEC strains heated in 7% fat ground beef (P < 0.05), but no non-O157 STEC strain had D55°C greater than the range observed for O157 STEC. D55°C was significantly different for strains within serogroups O45, O145, and O157 (P < 0.05). D55°C for non-O157 STEC strains in 15 and 27% fat ground beef were less than or equal to the range of D55°C for O157. D55°C for pathogen cocktails was not significantly different when measured in 7, 15, and 27% fat ground beef (P ≥ 0.05). D55°C of Salmonella in frankfurter batter was significantly less than for O157 and non-O157 STEC (P < 0.05). Thermal tolerance of pathogen cocktails in ground beef (7, 15, or 27% fat) and frankfurter batter was significantly less than for potential pathogen surrogates (P < 0.05). Results suggest that thermal processes in beef validated against E. coli O157:H7 have adequate lethality against non-O157 STEC, that thermal processes that target Salmonella destruction may not be adequate against STEC in some situations, and that the use of pathogen surrogates P. acidilactici and S. carnosus to validate thermal processing interventions in ground beef and frankfurter batter would be of limited utility to processors.

Some Like It Hot: Heat Resistance of Escherichia coli in Food

“…An increased fat content in food products increased the heat resistance of E. coli in some studies (Line et al, 1991; Huang et al, 1992; Ahmed et al, 1995; Smith et al, 2001; Liu et al, 2015), while other studies reported decreased resistance, no effect, or strain-specific effects (Kotrola and Conner, 1997; Vasan et al, 2014; Liu et al, 2015). The potential direct effects of fat on heat resistance of E. coli are confounded by the strong effect of fat on heat transfer in solid foods.…”

Consumer preference of ground beef patties with varying percentages of finely textured beef

“…When ground beef fat content increased from 7 to 30% and patties were frozen, then thawed or refrigerated before cooking on a gas grill, there was a greater inactivation of E. coli O157:H7. Additionally, thermal processing steps used to eliminate E. coli O157:H7 can also be utilized to eliminate non-O157 STEC, only a few strains may posses a higher thermal tolerance and need a different type of processing (Vasan et al, 2014). Furthermore, irradiation treatment has been found to eliminate E. coli O157:H7, consequently the USDA has created regulations on irradiation of beef products to eliminate these pathogens (Vogt and Dippold, 2005).…”

“…These guidelines outline a minimum time and temperature combination that must be met to achieve a 6.5-log reduction of Salmonella in beef products (Vasan et al, 2014). Salmonella causes an estimated one million cases of food born illness, which results in nearly 400 deaths a year (Scallan et al, 2011).…”

The Relative Efficacy of Thermal and Acidification Stresses on the Survival of E. coli O157:H7, Salmonella, and Listeria Monocytogenes in Ground Beef

“…The authors found significant differences in decimal reduction of E. coli among various strains at 55 °C. The time for Salmonella decimal reduction was found to be significantly less than O157 and non-O157 Shiga toxigenic E. coli (Vasan et al, 2014).…”

“…The inactivation results of foodborne pathogens in ground beef by the energy of radio frequency indicated that the cooking of meatballs with the combination of radio frequency and convection cooking reduced the levels of E. coli O157:H7, Salmonella, and Listeria monocytogenes to the non-detectable levels in 5.5 minutes (Schlisselberg et al, 2013). It has also been reported that the efficacy of treatments with regards to pathogen inactivation changes with products and strains (Vasan, Geier, Ingham, & Ingham, 2014). The authors found significant differences in decimal reduction of E. coli among various strains at 55 °C.…”