热胁迫和培养温度对大肠杆菌抗热性的影响

研究大肠杆菌O157:H7 ATCC 43889经50、60 ℃和70 ℃反复多次热胁迫处理与在10、28、36 ℃和45 ℃的条件下生长培养后对其80 ℃抗热性的影响。分别对ATCC 43889进行50、60 ℃和70 ℃的热胁迫，研究在一定的热力致死温度条件下杀死某细菌数量90%所需要的时间（D值）的变化，观察ATCC 43889热胁迫前后菌落形态和个体形态的变化；将ATCC 43889置于10、28、36 ℃和45 ℃培养至稳定期，分别测定其在80 ℃的存活量，再利用Weibull模型拟合其在80 ℃的热致死曲线。结果表明，50、60 ℃和70 ℃热胁迫处理均可诱导ATCC 43889抗热性增加，经10 次热胁迫并传代培养后，其D值分别为第1次热胁迫处理后的1.88、2.38 倍和8.18 倍，D值随热处理次数的增加不断增大，说明胁迫温度越高，D值越大，其抗热性越强；经过60 ℃和70 ℃热胁迫后，ATCC 43889菌落形态和个体形态与对照组相比差异显著；在80 ℃，ATCC 43889的致死曲线表明，胁迫温度越高，其抗热性越强（P＜0.05）；在10～45 ℃培养，随培养温度的升高，ATCC 43889的抗热性显著增加（P＜0.05）。利用Weibull模型可以较好地拟合ATCC 43889经过50、60 ℃和70 ℃热胁迫处理10 次后与10、28、36 ℃和45 ℃培养后在80 ℃的抗热性曲线，随着胁迫温度和培养温度的升高，ATCC 43889的抗热性都呈增加趋势。综上，一定热处理与培养温度可胁迫诱导大肠杆菌ATCC 43889抗性热增强和形态的变化。

Effects of Heat Stress and Growth Temperature on the Heat Resistance of Escherichia coli

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.