Heat Resistance of Escherichia coli O157:H7 in a Nutrient Medium and in Ground Beef Patties as Influenced by Storage and Holding Temperatures

Abstract

Stationary-phase cultures of Escherichia coli O157:H7 were inoculated into tryptic soy broth, sealed in vials, and stored at -18 degrees C for 1, 8, and 15 days, or 3 or 15 degrees C for 3, 6, and 9 h. Thermal resistance was determined at 55 degrees C. Each storage treatment was repeated with additional holding at 23 or 30 degrees C for 1, 2, 3, or 4 h prior to heating to simulate potential temperature abuse during handling. Cultures under treatments enabling the growth of E. coli O157:H7 were generally more heat sensitive than those held at temperatures which restricted growth or enabled growth to stationary phase. Cultures stored frozen (-18 degrees C) without holding at elevated temperatures had greater heat resistance than those stored under refrigeration (3 degrees C) or at 15 degrees C. Subsequent holding of frozen cultures at 23 or 30 degrees C resulted in a decrease in heat resistance. To determine whether these responses would be observed under typical commercial preparation procedures, ground beef patties were inoculated with E. coli O157:H7 and stored at 3 or 15 degrees C for 9 h or at -18 degrees C for 8 d and then held at 21 or 30 degrees C for 0 or 4 h. Patties were grilled to an internal temperature of 54.4 degrees C (130 degrees F), 62.8 degrees C (145 degrees F), or 68.3 degrees C (155 degrees F). Cultures were most resistant in frozen patties, while cultures in patties stored at 15 degrees C were the most heat sensitive. Holding patties at 21 or 30 degrees C prior to grilling resulted in increased sensitivity. Storage and holding temperatures similar to those encountered in food service may influence the ability of E. coli O157:H7 to survive heat treatments.

The Response ofCampylobacter jejunito Low Temperature Differs from That ofEscherichia coli

“…Previous studies have also shown that prior exposure of E. coli to refrigeration temperatures leads to an increased sensitivity to subsequent heat exposure (21). Cold exposure had subtly different effects on the heat tolerance of the two C. jejuni strains.…”

Thermal inactivation ofEscherichia coliO157:H7

“…Storage conditions can also affect heat resistance. Whilst Jackson et al (1996) reported that storage at 3°C decreased heat resistance, and that the heat resistance of cells in meat that had been stored frozen was greater than for equivalent samples stored under refrigeration, Stringer et al (2000) found that holding cells in TSB at 2°C for 10 d brought THERMAL DEATH OF E. COLI 0157: H7 83S about a small increase in heat resistance (Fig. 3).…”

“…Heat resistance was greater when cells were in the stationary rather than the logarithmic growth phase (Todd et al 1993;Jackson et al 1996;Kaur et al 1998), and when cells were grown at 37 or 40°C rather than 10, 23, 25 or 30°C (jackson et al 1996;Kaur et al 1998;Semanchek and Golden 1998;Fig. 3).…”

“…The highest z-value was 7·29°C for cells heated in chicken slurry (Betts et al 1993) and the lowest value for serotype 0157:H7 was Table 1 for parameters of these lines), and the broken line on (a) indicates the 'line of safety' corresponding to a ID reduction from the recommendations of the ACMSF (1995). Data are from: Doyle and Schoeni 1984;Line et al 1991;Pierson 1992, 1993;Abdul-Raouf et al 1993;Betts et al 1993;Nishikawa et al 1993;Todd et al 1993;Ahmed and Conner 1995;Ahmed et al 1995;Beuchat 1995, 1996;Czechowicz et al 1996;Jackson et al 1996;Splittstoesser et al 1996;Teo et al 1996;Blackburn et al 1997;Juneja et al 1997a;Kotrola and Conner 1997;Kotrola et al 1997;Orta-Ramirez et al 1997;Williams and Ingham 1997;Clavero et al 1998;Ingham and Uljas 1998;Juneja et al 1998;Kaur et al 1998;~intavalla et al 1998;Semanchek and Golden 1998;Williams and Ingham 1998;Veeramuthu et al 1998;Duffy et al 1999;George et al 1999;Stringer et al 2000 3·9°C for cells heated in ground beef and enumerated on MEMB (Clavero et al 1998). A z-value of 3·5°C was reported for a VTEC strain of serotype 0157:NM in beef (Todd et al 1993).…”

On the Optimal Control of Contact-Cooking Processes

“…McDonald"s has restaurants in over 100 countries serving several million hamburgers per day. In recent years, the cooking process of hamburger patties has been brought to question due to several outbreaks of food poisoning [4][5][6][7][8] . In the research presented here, hamburguer patties were taken as a case study, useful in developing applications for industrial manufacturing of a wide variety of foods that are non-homogeneous in nature, e.g.…”