University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, Canada.
University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, Canada.
Int J Food Microbiol. 2015 Jul 16;205:16-22. doi: 10.1016/j.ijfoodmicro.2015.03.028. Epub 2015 Mar 31.
Many strains of verotoxigenic Escherichia coli (VTEC) are highly resistant to pressure. To facilitate future studies to improve the elimination of VTEC by pressure processing of food, this study developed and validated a cocktail of non-pathogenic strains of E. coli with equal or higher resistance to pressure when compared to pressure resistant strains of VTEC. Strains of E. coli obtained from a beef processing plant were screened for their resistance to heat and pressure. Treatments were carried out in LB broth. Cell counts of 3 out of 16 strains were reduced by 5-6 log (cfu/mL) after 30 min at 60 °C, and cell counts of 10 out of 16 strains were reduced by 5-6 log (cfu/mL) after 30 min at 40 °C and 400 MPa. All highly heat resistant strains were also pressure resistant but not all pressure resistant strains were also heat resistant. Pressure resistant and -sensitive strains of E. coli were treated in presence of 0 or 2% NaCl and at 3, 20, or 40 °C. The effect of these parameters on the lethality of pressure treatments was comparable for all strains. The addition of 2% NaCl did not increase pressure resistance. The bactericidal effect of treatments at 3 and 20 °C and 600 MPa was comparable but inactivation of E. coli was faster at 40 °C and 600 MPa. The resistance to treatment with 600 MPa at 20 °C of a cocktail of 5 non-pathogenic strains of E. coli was compared to a 5 strain cocktail of pressure resistant VTEC. Treatments were performed in ground beef containing 15% fat. Survival and sublethal injury of the two cocktails was comparable; cell counts of beef inoculated with either cocktail were reduced by about 4 log (cfu/mL) after 30 min of treatment. In conclusion, this study validated a cocktail of non-pathogenic strains of E. coli for use as surrogate organisms in studies on the elimination of E. coli by pressure.
许多产肠毒素性大肠杆菌 (VTEC) 菌株对压力具有很强的抵抗力。为了促进未来通过食品压力处理来消除 VTEC 的研究，本研究开发并验证了一种由具有与 VTEC 耐压力菌株相等或更高压力抗性的非致病性大肠杆菌菌株组成的鸡尾酒。从牛肉加工厂获得的大肠杆菌菌株被筛选出对热和压力的抗性。在 LB 肉汤中进行处理。在 60°C 下 30 分钟后，16 株中有 3 株的细胞计数减少了 5-6 个对数（cfu/mL），在 40°C 和 400 MPa 下 30 分钟后，16 株中有 10 株的细胞计数减少了 5-6 个对数（cfu/mL）。所有高耐热菌株也具有耐压性，但并非所有耐压菌株也具有耐热性。在存在 0 或 2%NaCl 的情况下处理耐压和敏感的大肠杆菌菌株，并在 3、20 或 40°C 下处理。这些参数对所有菌株的压力处理致死效果的影响相当。添加 2%NaCl 不会增加耐压性。在 3 和 20°C 和 600 MPa 下处理的杀菌效果相当，但在 40°C 和 600 MPa 下大肠杆菌的失活速度更快。比较了 5 株非致病性大肠杆菌菌株和 5 株耐压 VTEC 菌株组成的鸡尾酒在 20°C 和 600 MPa 下处理的抗性。在含有 15%脂肪的碎牛肉中进行处理。两种鸡尾酒的存活和亚致死损伤相当；用任一鸡尾酒接种的牛肉的细胞计数在 30 分钟的处理后减少了约 4 个对数（cfu/mL）。总之，本研究验证了一种由非致病性大肠杆菌菌株组成的鸡尾酒可作为替代生物体，用于研究通过压力消除大肠杆菌。
