Listeria (L.) monocytogenes strains show a high diversity regarding stress tolerance and virulence potential. Genome studies have mainly focused on specific sequence types (STs) predominantly associated with either food or human listeriosis. This study focused on the prevalent ST155, showing equal distribution among clinical and food isolates. We evaluated the virulence potential of 20 ST155 strains and performed comparative genomic analysis of 130 ST155 strains isolated from food, food processing environments and human listeriosis cases in different countries and years. The in vitro virulence assays using human intestinal epithelial Caco2 and hepatocytic HEPG2 cells showed an impaired virulence phenotype for six of the 20 selected ST155 strains. Genome analysis revealed no distinct clustering of strains from the same source category (food, food processing environment, and clinical isolates). All strains harbored an intact inlA and inlB locus, except four strains, which had an internal deletion in the inlA gene. All strains harbored LIPI-1, but prfA was present in a longer variant in six strains, all showing impaired virulence. The longer PrfA variant resulted in lower expression of inlA, inlB, and prfA, and no expression of hly and actA. Regarding stress-related gene content, SSI-1 was present, whereas qacH was absent in all strains. 34.6% of the strains harbored a plasmid. All but one ST155 plasmids showed high conservation and harbored cadA2, bcrABC, and a triphenylmethane reductase. This study contributes to an enhanced understanding of L. monocytogenes ST155 strains, being equally distributed among isolates from humans, food, and food processing environments. The conservation of the present genetic traits and the absence of unique inherent genetic features makes these types of STs especially interesting since they are apparently equally adapted to the conditions in food processing environments, as well as in food as to the human host environment. However, a ST155-specific mutation resulting in a longer PrfA variant impaired the virulence potential of several ST155 strains.

中文翻译：

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李斯特菌155型单核细胞增生李斯特菌的毒力鉴定和比较基因组学

单核细胞增生李斯特菌菌株在胁迫耐受性和毒力方面表现出高度的多样性。基因组研究主要集中于主要与食物或人类李斯特菌病相关的特定序列类型（ST）。这项研究的重点是流行的ST155，显示临床和食品分离物中的均等分布。我们评估了20株ST155菌株的毒力潜力，并对从不同国家和年份的食品，食品加工环境和人类李斯特菌病病例中分离出的130株ST155菌株进行了比较基因组分析。使用人肠上皮Caco2和肝细胞HEPG2细胞进行的体外毒力测定显示，在所选的20种ST155菌株中，有六种的毒力表型受损。基因组分析显示，同一来源类别（食物，食品加工环境和临床分离株）。除四个菌株外，所有菌株均具有完整的inlA和inlB基因座，它们在inlA基因中具有内部缺失。所有菌株均携带LIPI-1，但prfA在6个菌株中以更长的变异体形式存在，均显示出毒性降低。较长的PrfA变体导致inlA，inlB和prfA的较低表达，而没有hly和actA的表达。关于应激相关基因的含量，存在SSI-1，而在所有菌株中都没有qacH。34.6％的菌株带有质粒。除一个ST155质粒外，其他所有质粒均显示出较高的保守性，并带有cadA2，bcrABC和三苯甲烷还原酶。这项研究有助于增进对单核细胞增生李斯特菌ST155菌株的了解，这些菌株在人类，食品和食品加工环境的分离物中均等分布。当前遗传特性的保护以及独特的固有遗传特征的缺乏使得这些类型的ST特别有趣，因为它们显然同样适用于食品加工环境以及食品以及人类宿主环境中的条件。然而，导致更长的PrfA变体的ST155特异性突变削弱了几种ST155菌株的毒力潜能。