Liu Yang, Gill Alex, McMullen Lynn, Gänzle Michael G
University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, Canada.
Health Canada/Sante Canada, Microbiology Research Division, Bureau of Microbial Hazards, Ottawa, Canada.
J Food Prot. 2015 Jan;78(1):111-20. doi: 10.4315/0362-028X.JFP-14-267.
This study evaluated the heat and pressure resistance of 112 strains of Escherichia coli, including 102 strains of verotoxigenic E. coli (VTEC) representing 23 serotypes and four phylogenetic groups. In an initial screening, the heat and pressure resistance of 100 strains, including 94 VTEC strains, were tested in phosphate-buffered saline (PBS). Treatment at 60°C for 5 min reduced cell counts by 2.0 to 5.5 log CFU/ml; treatment at 600 MPa for 3 min at 25°C reduced the cell counts by 1.1 to 5.5 log CFU/ml. Heat or pressure resistance did not correlate to the phylogenetic group or the serotype. A smaller group of E. coli strains was evaluated for heat and pressure resistance in Luria-Bertani (LB) broth. Generally, the levels of heat resistance of E. coli strains in LB and PBS were similar; however, the levels of pressure resistance observed for treatments in LB broth or PBS were variable. The cell counts of pressure-resistant strains of VTEC were reduced by less than 1.5 log CFU/ml after treatment at 600 MPa for 3 min. E. coli strains were also treated with 600 MPa for 3 min in ground beef or inoculated into beef patties and grilled to 63 or 71°C. The cell counts of the VTEC E. coli O26:H11 strain 05-6544 were reduced by 2 log CFU/g by pressure treatment in ground beef. The cell counts of the heat-resistant E. coli strain AW1.7 were reduced by 1.4 and 3.4 log CFU/g in beef patties grilled to internal temperatures of 63 and 71°C, respectively. The cell counts of E. coli 05-6544 were reduced by less than 3 and 6 log CFU/g in beef patties grilled to internal temperatures of 63 and 71°C, respectively. To study whether the composition of the beef patties influenced heat resistance, E. coli strains AW1.7, AW1.7 Δ pHR1, MG1655, and LMM1030 were mixed into beef patties containing 15 or 35% fat and 0 or 2% NaCl, and the patties were grilled to an internal temperature of 63°C. The highest heat resistance of E. coli was observed in patties containing 15% fat and 2% NaCl.
本研究评估了112株大肠杆菌的耐热性和耐压性，其中包括102株产志贺毒素大肠杆菌（VTEC），代表23种血清型和四个系统发育组。在初步筛选中，在磷酸盐缓冲盐水（PBS）中测试了100株菌株（包括94株VTEC菌株）的耐热性和耐压性。60°C处理5分钟可使细胞计数减少2.0至5.5 log CFU/ml；25°C下600 MPa处理3分钟可使细胞计数减少1.1至5.5 log CFU/ml。耐热性或耐压性与系统发育组或血清型无关。对一小群大肠杆菌菌株在Luria-Bertani（LB）肉汤中进行了耐热性和耐压性评估。一般来说，大肠杆菌菌株在LB和PBS中的耐热水平相似；然而，在LB肉汤或PBS中处理时观察到的耐压水平是可变的。在600 MPa处理3分钟后，耐压VTEC菌株的细胞计数减少不到1.5 log CFU/ml。大肠杆菌菌株还在绞碎牛肉中用600 MPa处理3分钟，或接种到牛肉饼中并烤至63或71°C。通过绞碎牛肉中的压力处理，VTEC大肠杆菌O26:H11菌株05-6544的细胞计数减少了2 log CFU/g。在烤至内部温度为63°C和71°C的牛肉饼中，耐热大肠杆菌菌株AW1.7的细胞计数分别减少了1.4和3.4 log CFU/g。在烤至内部温度为63°C和71°C的牛肉饼中，大肠杆菌05-6544的细胞计数分别减少了不到3和6 log CFU/g。为了研究牛肉饼的成分是否影响耐热性，将大肠杆菌菌株AW1.7、AW1.7 Δ pHR1、MG1655和LMM1030混入含有15%或35%脂肪以及0%或2% NaCl的牛肉饼中，并将牛肉饼烤至内部温度为63°C。在含有15%脂肪和2% NaCl的牛肉饼中观察到大肠杆菌的最高耐热性。
