Listeria monocytogenes is a pathogen mostly associated with the consumption of ready-to-eat foods and can cause severe disease and death. It can be introduced into food chains from raw materials, but often the contamination source is the food production environment, where certain clones can persist for years. In the meat chain, ST9 is one of the most commonly encountered L. monocytogenes sequence types, and for effective source tracking, the divergence and spread of ST9 must be understood. In this study, whole-genome sequencing (WGS) was used to characterize and track 252 L. monocytogenes ST9 isolates collected from four Norwegian meat processing plants between 2009 and 2017. The isolates formed distinct clusters relative to genomes found in public databases, and all but three isolates clustered into two major clonal populations. Different contamination patterns were revealed, e.g., evidence of contamination of two factories with a clone that diverged from its ancestor in the late 1990s through a common source of raw materials; breach of hygienic barriers within a factory, leading to repeated detection of two clones in the high-risk zone during a 4- to 6-year period; entry through the purchase and installation of second-hand equipment harboring a previously established clonal population; and spreading and diversification of two clones from two reservoirs within the same production room over a 9-year period. The present work provides data on the diversity of ST9, which is crucial for epidemiological investigations and highlights how WGS can be used for source tracking within food processing factories.

中文翻译：

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肉类加工行业单核细胞增生李斯特菌ST9分离株的深度纵向研究：使用全基因组测序解决多样性和传播方式。

单核细胞增生李斯特菌是一种致病菌，主要与食用即食食品有关，可能导致严重的疾病和死亡。它可以从原材料引入食品链，但污染源通常是食品生产环境，某些克隆可能会持续多年。在肉链中，ST9是最常见的单核细胞增生李斯特菌序列类型之一，为了有效地追踪源，必须了解ST9的扩散和扩散。在这项研究中，全基因组测序（WGS）用于表征和追踪252个单核细胞增生李斯特菌2009年至2017年间，从四个挪威肉类加工厂收集到的ST9分离株。相对于公共数据库中发现的基因组，分离株形成了不同的簇，除三个分离株外，所有分离株均聚集成两个主要的克隆种群。揭示了不同的污染模式，例如，有证据表明两家工厂受到克隆的污染，该克隆在1990年代后期通过共同的原材料来源脱离了其祖先。违反工厂内部的卫生标准，导致在4至6年的时间内反复发现高风险区的两个克隆；通过购买和安装具有先前确定的克隆种群的二手设备进入；在9年的时间内，在同一生产室内从两个储层中克隆出两个克隆，并使其多样化。