Food, Nutrition and Health, The University of British Columbia, Vancouver, British Columbia, Canada.
National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark.
Int J Food Microbiol. 2019 Oct 2;306:108262. doi: 10.1016/j.ijfoodmicro.2019.108262. Epub 2019 Jul 20.
In this study, we show that growth and prolonged storage of Listeria monocytogenes at 4 °C can promote the selection of variants with enhanced cold and heat tolerance. Enhanced cold-tolerance (ECT) variants (n = 12) were successfully isolated from a strain with impaired cold growth abilities following 84 days of storage at 4 °C in brain heart infusion broth (BHIB). Whole genome sequencing, membrane fatty acid analysis, and stress tolerance profiling were performed on the parent strain and two ECT variants: one displaying regular-sized colonies and the other displaying small colonies when grown at 37 °C on BHI agar. Under cold stress conditions, the parent strain exhibited an impaired ability to produce branched-chain fatty acids which are known to be important for cold adaptation in L.monocytogenes. The ECT variants were able to overcome this limitation, a finding which is hypothesized to be associated with the identification of two independent single-nucleotide polymorphisms in genes encoding subunits of acetyl-coA carboxylase, an enzyme critical for fatty acid biosynthesis. While the ECT phenotype was not found to be associated with improved salt (BHIB + 6% NaCl, 25 °C), acid (BHIB pH 5, 25 °C) or desiccation (33% RH, 20 °C) tolerance, the small-colony variant exhibited significantly (p < 0.05) enhanced heat tolerance at 52 °C in buffered peptone water compared to the parent strain and the other variant. The results from this study demonstrate that the continuous use of refrigeration along the food-supply chain has the potential to select for L.monocytogenes variants with enhanced cold and heat tolerance, highlighting the impact that microbial intervention strategies can have on the evolution of bacterial strains and likewise, food safety.
在这项研究中，我们表明，在 4°C 下生长和长时间储存李斯特菌可以促进选择具有增强的耐寒和耐热性的变体。在 4°C 的脑心浸液肉汤（BHIB）中储存 84 天后，从生长能力受损的菌株中成功分离出增强耐寒性（ECT）变体（n=12）。对亲本菌株和两个 ECT 变体（一个显示常规大小的菌落，另一个在 BHI 琼脂上 37°C 下生长时显示小菌落）进行了全基因组测序、膜脂肪酸分析和应激耐受谱分析。在冷应激条件下，亲本菌株表现出产生支链脂肪酸的能力受损，而支链脂肪酸已知对李斯特菌的冷适应很重要。ECT 变体能够克服这一限制，这一发现被假设与在编码乙酰辅酶 A 羧化酶亚基的基因中发现两个独立的单核苷酸多态性有关，乙酰辅酶 A 羧化酶是脂肪酸生物合成的关键酶。虽然 ECT 表型与提高盐度（BHIB+6%NaCl，25°C）、酸度（BHIB pH 5，25°C）或干燥度（33%RH，20°C）的耐受性无关，但与亲本菌株和另一个变体相比，小菌落变体在缓冲蛋白胨水中在 52°C 时表现出显著（p<0.05）增强的耐热性。本研究结果表明，沿食品供应链持续使用冷藏有选择出具有增强耐寒和耐热性的李斯特菌变体的潜力，突出了微生物干预策略对细菌菌株进化的影响，同样对食品安全也有影响。
