Department of Food Science and Technology, National University of Singaporegrid.4280.e, Singapore, Singapore.
National University of Singaporegrid.4280.e (Suzhou) Research Institute, Suzhou, Jiangsu, People's Republic of China.
Appl Environ Microbiol. 2022 Apr 12;88(7):e0009822. doi: 10.1128/aem.00098-22. Epub 2022 Mar 14.
Escherichia coli outbreaks linked to wheat flour consumption have kept emerging in recent years, which necessitated an antimicrobial step being incorporated into the flour production process. The objectives of this study were to holistically evaluate the sanitizing efficacy of thermal treatment at 60 and 70°C against the "big six" E. coli strains (O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) in wheat flour and to assess the strain-specific metabolic responses using nuclear magnetic resonance (NMR) spectroscopy. The 70°C treatment temperature indiscriminatingly inactivated all strains by over 4.3-log CFU/g within 20 min, suggesting the high sanitization effectiveness of this treatment temperature, whereas the treatment at 60°C inactivated the strains to various degrees during the 1-h process. The most resistant strains at 60°C, O26 and O45, were characterized by amino acid and sugar depletion, and their high resistance was attributed to the dual effects of activated heat shock protein (HSP) synthesis and promoted glycolysis. O121 also demonstrated these metabolic changes, yet its thermal resistance was largely impaired by the weakened membrane structure and diminished osmotic protection due to phosphorylcholine exhaustion. In contrast, O111, O145, and O103 presented a substantial elevation of metabolites after stress at 60°C; their moderate thermal resistance was mainly explained by the accumulation of amino acids as osmolytes. Overall, the study enhanced our understanding of the metabolic responses of big six E. coli to heat stress and provided a model for conducting NMR-based metabolomic studies in powdered food matrices. "Big six" Escherichia coli strains have caused several outbreaks linked to wheat flour consumption in the last decade, revealing the vital importance of adopting an antimicrobial treatment during the flour production process. Therefore, the present study was carried out to evaluate the efficacy of a typical sanitizing approach, thermal treatment, against the big six strains in wheat flour along with the underlying antimicrobial mechanisms. Findings showed that thermal treatment at 60 and 70°C could markedly mitigate the loads of all strains in wheat flour. Moreover, activated heat shock protein synthesis combined with expedited glycolysis and enhanced osmotic protection were identified as two major metabolic alteration patterns in the E. coli strains to cope with the heat stress. With the responses of big six in wheat flour to thermal treatment elucidated, scientific basis for incorporating a thermal inactivation step in wheat flour production was provided.
近年来，与小麦粉消费相关的大肠杆菌暴发事件不断出现，这使得在面粉生产过程中必须采取抗菌措施。本研究的目的是全面评估 60 和 70°C 热处理对“六大”大肠杆菌（O26：H11、O45：H2、O103：H11、O111、O121：H19 和 O145）在小麦粉中的消毒效果，并使用核磁共振（NMR）光谱评估菌株特异性代谢反应。70°C 的处理温度在 20 分钟内使所有菌株的失活程度超过 4.3-log CFU/g，表明该处理温度具有很高的消毒效果，而 60°C 的处理在 1 小时的过程中使菌株失活程度不同。在 60°C 下最具抗性的菌株 O26 和 O45 的特点是氨基酸和糖的消耗，其高抗性归因于激活热休克蛋白（HSP）合成和促进糖酵解的双重作用。O121 也表现出这些代谢变化，但由于磷酸胆碱耗尽导致膜结构减弱和渗透保护减少，其耐热性受到很大影响。相比之下，O111、O145 和 O103 在 60°C 下受到压力后代谢物大量增加；它们的中等耐热性主要归因于氨基酸作为渗透剂的积累。总的来说，该研究增强了我们对“六大”大肠杆菌对热应激的代谢反应的理解，并为在粉状食品基质中进行基于 NMR 的代谢组学研究提供了模型。“六大”大肠杆菌菌株在过去十年中引发了几起因与小麦粉消费相关的暴发事件，这凸显了在面粉生产过程中采用抗菌处理的重要性。因此，本研究旨在评估典型消毒方法（热处理）对小麦粉中“六大”菌株的功效以及潜在的抗菌机制。研究结果表明，60 和 70°C 的热处理可以显著减轻小麦粉中所有菌株的负荷。此外，发现激活热休克蛋白合成与加快糖酵解和增强渗透保护一起，被确定为大肠杆菌菌株应对热应激的两种主要代谢改变模式。阐明了“六大”在小麦粉中对热处理的反应，为在小麦粉生产中加入热失活步骤提供了科学依据。
