关键词: 大肠杆菌, 热胁迫, 培养温度, Weibull模型, 抗热性

Abstract: The effects of repeated heat stress at 50, 60 or 70 ℃ and different growth temperatures (10, 28, 36 and 45 ℃) on the resistance of Escherichia coli O157:H7 ATCC 43889 to high temperature of 80 ℃ were studied. The change in D value (time necessary to kill 90% of microorganisms) was determined during repeated heat stress, and the changes in colonial and cellular morphology were observed. The survival rate of this strain, grown to the stationary phase at different temperatures, was measured at 80 ℃. The thermal death curves were fitted to the Weibull model. The experimental results showed that the heat resistance of E. coli ATCC 43889 was increased by heat stress at each temperature tested. The D values of the passaged cells subjected to heat stress at 50, 60 or 70 ℃ 10 times were 1.88, 2.38 and 8.18 times higher than those undergoing one cycle of heat stress, respectively, D value was increased with increasing number of heat stress cycles. This demonstrates that heat stress at a higher temperature resulted in a larger D value and stronger heat resistance. After heat stress at 60 or 70 ℃, significant variations in colonial and cellular morphology were found relative to the control group. The thermal death curve at 80 ℃ also showed that the higher the stress temperature, the stronger the heat resistance (P < 0.05). The heat resistance was increased with the increase in growth temperature from 10 to 45 ℃ (P < 0.05). The Weibull model could well fit the heat resistance data after heat stress at 50, 60 or 70 ℃ for 10 times and growth at 10, 28, 36 or 45 ℃. The heat resistance increased with increasing either stress temperature or growth temperature. In conclusion, certain heat treatments and incubation temperatures can cause enhanced heat resistance and morphological changes in E. coli ATCC 43889.

Key words: Escherichia coli, heat stress, growth temperature, Weibull model, heat resistance