Nestlé Research, Vers-Chez-les-Blanc 26, 1000, Lausanne, Switzerland.
Nestlé Research, EPFL Innovation Park, 1015, Lausanne, Switzerland.
Sci Rep. 2021 Apr 14;11(1):8144. doi: 10.1038/s41598-021-87330-8.
WGS is used to define if isolates are "in" or "out" of an outbreak and/or microbial root cause investigation. No threshold of genetic differences is fixed and the conclusions on similarity between isolates are mainly based on the knowledge generated from previous outbreak investigations and reported mutation rates. Mutation rates in Salmonella when exposed to food processing conditions are lacking. Thus, in this study, the ability of heat and dry stress to cause genetic changes in two Salmonella serotypes frequently isolated from low moisture foods was investigated. S. enterica serovars S. Agona ATCC 51,957 and S. Mbandaka NCTC 7892 (ATCC 51,958) were repeatedly exposed to heat (90 °C for 5 min) in a low water activity and high fat matrix. No increased fitness of the strains was observed after 10 repeated heat treatments. However, genetic changes were introduced and the number of genetic differences increased with every heat treatment cycle. The genetic changes appeared randomly in the genome and were responsible for a population of diverse isolates with 0 to 28 allelic differences (0 to 38 SNPs) between them. This knowledge is key to interpret WGS results for source tracking investigations as part of a root cause analysis in a contamination event as isolates are exposed to stress conditions.
WGS 用于确定分离株是否处于暴发“内部”或“外部”以及/或进行微生物根本原因调查。没有固定的遗传差异阈值，关于分离株之间相似性的结论主要基于以前暴发调查和报告的突变率产生的知识。在暴露于食品加工条件下时，沙门氏菌的突变率是未知的。因此，在这项研究中，研究了热和干燥应激对两种经常从低水分食品中分离出的沙门氏菌血清型引起遗传变化的能力。反复将肠炎沙门氏菌血清型 S. Agona ATCC 51,957 和 S. Mbandaka NCTC 7892（ATCC 51,958）暴露于低水活度和高脂肪基质中的 90°C 5 分钟。经过 10 次重复的热处理后，未观察到菌株适应性增加。然而，引入了遗传变化，并且随着每个热处理循环，遗传差异的数量增加。遗传变化随机出现在基因组中，导致存在具有 0 到 28 个等位基因差异（0 到 38 个 SNP）的多样化分离株群体。这一知识是解释 WGS 结果的关键，因为在污染事件的根本原因分析中，作为来源追踪调查的一部分，分离株会暴露于应激条件下。
