Unlike most   Salmonella enterica   subsp.   diarizonae  , which are predominantly associated with cold-blooded animals such as reptiles, the serovar IIIb 61:k:1,5,(7) (termed SASd) is regarded as host-adapted to sheep. The bacterium is rarely associated with disease in humans but, nevertheless, SASd isolates are sporadically obtained from human clinical samples. It is unclear whether these transmissions are directly linked to sheep or whether transmissions may, for example, occur through other domestic animals also carrying SASd. For this reason, we utilized whole-genome sequencing to investigate a set of 119 diverse SASd isolates, including sheep-associated and human-associated isolates, as well as isolates obtained from other matrices. We discovered that serovar IIIb 61:k:1,5,(7) is composed of two distinct lineages defined by their sequence types ST432 and ST439. These two lineages are distinguished by a number of genetic features, as well as their prevalence and reservoir. ST432 appears to be the more prevalent sequence type, with the majority of isolates investigated in this study belonging to ST432. In contrast, only a small number of isolates were attributed to ST439. While ST432 isolates were of sheep, human or other origin, all ST439 isolates with source information available, were obtained from human clinical samples. Regarding their genetic features, lineage ST432 shows increased pseudogenization, harbours a virB/D4 plasmid that encodes a type IV secretion system (T4SS) and does not possess the iro gene cluster, which encodes a salmochelin siderophore for iron acquisition. These characteristics likely contribute to the ability of ST432 to persistently colonize the intestines of sheep. Furthermore, we found isolates of the lineage ST432 to be highly clonal, with little variation over the sampling period of almost 20 years. We conclude from the genomic comparisons that SASd underlies a microevolutionary process and that it is specifically lineage ST432 that should be considered as host-adapted to sheep.

中文翻译：

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肠沙门氏菌亚种的比较基因组学。diarizonae serovar 61:k:1,5,(7) 揭示了 ST432 的谱系特异性宿主适应

与大多数 肠沙门氏菌 亚种不同。 diarizonae ，主要与爬行动物等冷血动物有关，    血清型 IIIb 61:k:1,5,(7)（称为 SASd）被认为是适应羊的宿主。该细菌很少与人类疾病相关，但是，SASd 分离株偶尔从人类临床样本中获得。目前尚不清楚这些传播是否与绵羊直接相关，或者是否可能通过其他也携带 SASd 的家畜进行传播。出于这个原因，我们利用全基因组测序来研究一组 119 种不同的 SASd 分离株，包括绵羊相关和人类相关的分离株，以及从其他基质中获得的分离株。我们发现血清型 IIIb 61:k:1,5,(7) 由两个不同的谱系组成，由它们的序列类型 ST432 和 ST439 定义。这两个谱系的区别在于许多遗传特征，以及它们的流行和储存库。ST432 似乎是更普遍的序列类型，本研究中研究的大多数分离株属于 ST432。相比之下，只有少数分离株归因于 ST439。虽然 ST432 分离株来自绵羊、人类或其他来源，但所有具有可用来源信息的 ST439 分离株均来自人类临床样本。关于它们的遗传特征，谱系 ST432 显示出增加的假性化，具有virB/D4质粒，编码 IV 型分泌系统 (T4SS)，不具有iro基因簇，该基因簇编码用于获取铁的沙门菌素铁载体。这些特征可能有助于 ST432 持续定植绵羊肠道的能力。此外，我们发现 ST432 谱系的分离株具有高度克隆性，在近 20 年的采样期内几乎没有变化。我们从基因组比较中得出结论，SASd 是一个微进化过程的基础，特别是 ST432 谱系应该被认为是适应羊的宿主。