Factors affecting the heat resistance of Escherichia coli O157 : H7

Abstract

Escherichia coli O157:H7 has been reported as being not particularly heat resistant. However, several factors which might increase its heat resistance have been investigated in this study using five strains. Increase in growth temperature to 40 degrees C, as found in the cow gut, heat-shock at sub-lethal temperatures of 42, 45, 48 and 50 degrees C, and variable heating rate (1 degree C min-1 to 23 degrees C min-1) had no dramatic effect on heat resistance. Growth phase had a marked impact on heat resistance; late stationary phase cells were more heat-resistant than were log phase cells. The difference in heat resistance between the two phases of growth became more pronounced when cells were resuspended in fresh nutrient broth; heat resistance of late stationary phase cells increased dramatically whereas no such effect was observed with log phase cells. The addition of polyphosphates to the heating medium did not increase heat resistance. A reduction in water activity of the heating medium from 0.995 to levels between 0.980 and 0.960 also resulted in a marked increase in heat resistance. This effect was more pronounced under conditions of extremely low water activity created by resuspending late stationary phase cells in sunflower oil. Survivors were detected even after a heat treatment at 60 degrees C for 1 h or 70 degrees C for 5 min. It can be confirmed that this serotype has no unusual heat resistance and that the heating environment markedly affects resistance.

Changes in Barotolerance, Thermotolerance, and Cellular Morphology throughout the Life Cycle of Listeria monocytogenes

“…3B), a finding that disagrees with previous studies (25,32). Perhaps stationary-phase cells in the present study still had not transitioned to resistant cocci (Fig.…”

Thermal inactivation ofEscherichia coliO157:H7

“…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).…”

Escherichia Coli O157:h7 in Food With Health-Related Risks

“…The bacterium is known to have a typical resistance to heat (Kaur et al, 1998). It can proliferate at a temperature range of 8-44.5 °C, with the optimal temperature for growth at 37 °C (Edwards & Fung, 2006).…”

“…It can proliferate at a temperature range of 8-44.5 °C, with the optimal temperature for growth at 37 °C (Edwards & Fung, 2006). Cooking beef thoroughly to 71 °C is effective in eliminating the organism (Doyle & Schoeni, 1984); although slow cooking of meats may not eradicate the organism as well as rapid heating (Edwards & Fung, 2006;Kaur et al, 1998). Regardless of pH and water activity, survival of E. coli was found to be better at 5 °C than at 20 or 30 °C in tryptic soy broth (TSB) (Rocelle et al, 1996).…”

“…Moreover, E. coli was found to survive but not grow during fermentation, drying, or subsequent storage at 4 °C for 2 months (Glass et al, 1992). The heatresistant property of E. coli O157:H7 is relative as it can be influenced by many other environmental factors, including growth phase, the amount of heat applied, the rate of heating and the water activity (Kaur et al, 1998). For instance, at 30 °C, inhibition of growth of E. coli O157:H7 in TSB was enhanced by reduction of the water activity (Rocelle et al, 1996) as well as increase of sodium chloride concentration (Jordan and Davies, 2001).…”