Lab of Beef Processing and Quality Control, College of Food Science and Engineering, Shandong Agricultural University, Tai'an, Shandong, 271018, PR China; National R&D Center for Beef Processing Technology, Tai'an, Shandong, 271018, PR China.
Lab of Beef Processing and Quality Control, College of Food Science and Engineering, Shandong Agricultural University, Tai'an, Shandong, 271018, PR China; National R&D Center for Beef Processing Technology, Tai'an, Shandong, 271018, PR China.
Food Microbiol. 2023 Jun;112:104244. doi: 10.1016/j.fm.2023.104244. Epub 2023 Feb 22.
The development of acid tolerance response (ATR) as a result of low pH in Escherichia coli O157:H7 (E. coli O157:H7) contaminating beef during processing is considered a major food safety concern. Thus, in order to explore the formation and molecular mechanisms of the tolerance response of E. coli O157:H7 in a simulated beef processing environment, the resistance of a wild-type (WT) strain and its corresponding ΔphoP mutant to acid, heat, and osmotic pressure was evaluated. Strains were pre-adapted under different conditions of pH (5.4 and 7.0), temperature (37 °C and 10 °C), and culture medium (meat extract and Luria-Bertani broth media). In addition, the expression of genes related to stress response and virulence was also investigated among WT and ΔphoP strains under the tested conditions. Pre-acid adaptation increased the resistance of E. coli O157:H7 to acid and heat treatment while resistance to osmotic pressure decreased. Moreover, acid adaptation in meat extract medium simulating slaughter environment increased ATR, whereas pre-adaptation at 10 °C reduced the ATR. Furthermore, it was shown that mildly acidic conditions (pH = 5.4) and the PhoP/PhoQ two-component system (TCS) acted synergistically to enhance acid and heat tolerance in E. coli O157:H7. Additionally, the expression of genes related to arginine and lysine metabolism, heat shock, and invasiveness was up-regulated, which revealed that the mechanism of acid resistance and cross-protection under mildly acidic conditions was mediated by the PhoP/PhoQ TCS. Both acid adaptation and phoP gene knockout reduced the relative expression of stx1 and stx2 genes which were considered as critical pathogenic factors. Collectively, the current findings indicated that ATR could occur in E. coli O157:H7 during beef processing. Thus, there is an increased food safety risk due to the persistence of tolerance response in the following processing conditions. The present study provides a more comprehensive basis for the effective application of hurdle technology in beef processing.
由于在加工过程中牛肉受到低 pH 值的影响，大肠杆菌 O157:H7（E. coli O157:H7）产生酸耐受反应（ATR），这被认为是一个主要的食品安全问题。因此，为了探索大肠杆菌 O157:H7 在模拟牛肉加工环境中的耐受反应的形成和分子机制，评估了野生型（WT）菌株及其相应的 ΔphoP 突变体对酸、热和渗透压的抗性。菌株在不同的 pH（5.4 和 7.0）、温度（37°C 和 10°C）和培养基（肉浸液和 LB 肉汤培养基）条件下进行预适应。此外，还在测试条件下研究了 WT 和 ΔphoP 菌株中与应激反应和毒力相关的基因表达。酸预适应增加了大肠杆菌 O157:H7 对酸和热处理的抗性，而对渗透压的抗性降低。此外，在模拟屠宰环境的肉浸液培养基中进行酸适应增加了 ATR，而在 10°C 下进行预适应则降低了 ATR。此外，结果表明，轻度酸性条件（pH = 5.4）和 PhoP/PhoQ 双组分系统（TCS）协同作用增强了大肠杆菌 O157:H7 的酸和热耐受性。此外，与精氨酸和赖氨酸代谢、热休克和侵袭性相关的基因表达上调，表明 PhoP/PhoQ TCS 介导了轻度酸性条件下的酸抗性和交叉保护机制。酸适应和 phoP 基因敲除都降低了 stx1 和 stx2 基因的相对表达，这被认为是关键的致病因素。总的来说，目前的研究结果表明，在牛肉加工过程中大肠杆菌 O157:H7 可能会发生 ATR。因此，在下一个加工条件下，由于耐受反应的持续存在，食品安全风险增加。本研究为有效应用障碍技术在牛肉加工中提供了更全面的基础。
