King Thea, Kocharunchitt Chawalit, Gobius Kari, Bowman John P, Ross Tom
From the ‡CSIRO Agriculture and Food, North Ryde, NSW 2113, Australia;
§Food Safety Centre, Tasmanian Institute of Agriculture, School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart TAS 7001, Australia.
Mol Cell Proteomics. 2016 Nov;15(11):3331-3347. doi: 10.1074/mcp.M116.063065. Epub 2016 Sep 11.
Enterohemeorrhagic Escherichia coli is a leading cause of foodborne illness, with the majority of cases linked to foods of bovine origin. Currently, no completely effective method for controlling this pathogen during carcass processing exists. Understanding how this pathogen behaves under those stress conditions experienced on the carcass during chilling in cold air could offer opportunities for development or improvement of effective decontamination processes. Therefore, we studied the growth kinetics and physiological response of exponential phase E. coli O157:H7 Sakai cultures upon an abrupt downshift in temperature and water activity (from 35 °C a 0.993 to 14 °C a 0.967). A parallel Biolog study was conducted to follow the phenotypic responses to 190 carbon sources. Exposure of E. coli to combined cold and water activity stresses resulted in a complex pattern of population changes. This pattern could be divided into two main phases, including adaptation and regrowth phases, based on growth kinetics and clustering analyses. The transcriptomic and proteomic studies revealed that E. coli exhibited a "window" of cell susceptibility (i.e. weaknesses) during adaptation phase. This included apparent DNA damage, the downregulation of molecular chaperones and proteins associated with responses to oxidative damage. However, E. coli also displayed a transient induction in the RpoE-controlled envelope stress response and activation of the master stress regulator RpoS and the Rcs phosphorelay system involved in colanic acid biosynthesis. Increased expression was observed for several genes and/or proteins involved in DNA repair, protein and peptide degradation, amino acid biosynthesis, and carbohydrate catabolism and energy generation. Furthermore, the Biolog study revealed reduced carbon source utilization during adaptation phase, indicating the disruption of energy-generating processes. This study provides insight into the physiological response of E. coli during exposure to combined cold and water activity stress, which could be exploited to enhance the microbiological safety of carcasses and related foods.
肠出血性大肠杆菌是食源性疾病的主要病因，大多数病例与源自牛的食品有关。目前，在胴体加工过程中不存在完全有效的控制这种病原体的方法。了解这种病原体在冷空气冷却过程中胴体所经历的那些应激条件下的行为，可能为开发或改进有效的去污工艺提供机会。因此，我们研究了指数期大肠杆菌O157:H7阪崎株培养物在温度和水分活度突然下降（从35℃、水分活度0.993降至14℃、水分活度0.967）时的生长动力学和生理反应。进行了一项平行的Biolog研究，以跟踪对190种碳源的表型反应。大肠杆菌暴露于寒冷和水分活度联合应激下导致了复杂的种群变化模式。基于生长动力学和聚类分析，这种模式可分为两个主要阶段，包括适应阶段和再生长阶段。转录组学和蛋白质组学研究表明，大肠杆菌在适应阶段表现出细胞易感性（即弱点）的“窗口”。这包括明显的DNA损伤、分子伴侣以及与氧化损伤反应相关的蛋白质的下调。然而，大肠杆菌在RpoE控制的包膜应激反应中也表现出短暂的诱导，以及参与柯氏酸生物合成的主要应激调节因子RpoS和Rcs磷酸转移系统的激活。参与DNA修复、蛋白质和肽降解、氨基酸生物合成以及碳水化合物分解代谢和能量产生的几个基因和/或蛋白质的表达增加。此外，Biolog研究表明，适应阶段碳源利用减少，表明能量产生过程受到破坏。这项研究深入了解了大肠杆菌在暴露于寒冷和水分活度联合应激期间的生理反应，这可用于提高胴体和相关食品的微生物安全性。
