Khajanchi Bijay K, Hasan Nur A, Choi Seon Young, Han Jing, Zhao Shaohua, Colwell Rita R, Cerniglia Carl E, Foley Steven L
U.S. Food and Drug Administration, National Center for Toxicological Research, Jefferson, AR, USA.
Center of Bioinformatics and Computational Biology, University of Maryland Institute of Advanced Computer Studies, University of Maryland, College Park, MD, USA.
BMC Genomics. 2017 Aug 2;18(1):570. doi: 10.1186/s12864-017-3954-5.
The degree to which the chromosomal mediated iron acquisition system contributes to virulence of many bacterial pathogens is well defined. However, the functional roles of plasmid encoded iron acquisition systems, specifically Sit and aerobactin, have yet to be determined for Salmonella spp. In a recent study, Salmonella enterica strains isolated from different food sources were sequenced on the Illumina MiSeq platform and found to harbor the incompatibility group (Inc) FIB plasmid. In this study, we examined sequence diversity and the contribution of factors encoded on the IncFIB plasmid to the virulence of S. enterica.
Whole genome sequences of seven S. enterica isolates were compared to genomes of serovars of S. enterica isolated from food, animal, and human sources. SeqSero analysis predicted that six strains were serovar Typhimurium and one was Heidelberg. Among the S. Typhimurium strains, single nucleotide polymorphism (SNP)-based phylogenetic analyses revealed that five of the isolates clustered as a single monophyletic S. Typhimurium subclade, while one of the other strains branched with S. Typhimurium from a bovine source. DNA sequence based phylogenetic diversity analyses showed that the IncFIB plasmid-encoded Sit and aerobactin iron acquisition systems are conserved among bacterial species including S. enterica. The IncFIB plasmid was transferred to an IncFIB plasmid deficient strain of S. enterica by conjugation. The transconjugant SE819::IncFIB persisted in human intestinal epithelial (Caco-2) cells at a higher rate than the recipient SE819. Genes of the Sit and aerobactin operons in the IncFIB plasmid were differentially expressed in iron-rich and iron-depleted growth media.
Minimal sequence diversity was detected in the Sit and aerobactin operons in the IncFIB plasmids present among different bacterial species, including foodborne Salmonella strains. IncFIB plasmid encoded factors play a role during infection under low-iron conditions in host cells.
染色体介导的铁摄取系统对许多细菌病原体毒力的贡献程度已得到明确界定。然而，质粒编码的铁摄取系统，特别是 Sit 和气杆菌素，对沙门氏菌属的功能作用尚未确定。在最近的一项研究中，从不同食物来源分离的肠炎沙门氏菌菌株在 Illumina MiSeq 平台上进行了测序，发现含有不相容群（Inc）FIB 质粒。在本研究中，我们检查了 IncFIB 质粒上编码的因子的序列多样性及其对肠炎沙门氏菌毒力的贡献。
将七株肠炎沙门氏菌分离株的全基因组序列与从食物、动物和人类来源分离的肠炎沙门氏菌血清型的基因组进行了比较。SeqSero 分析预测，六株菌株为鼠伤寒血清型，一株为海德堡血清型。在鼠伤寒沙门氏菌菌株中基于单核苷酸多态性（SNP）的系统发育分析表明，五株分离株聚为一个单系的鼠伤寒沙门氏菌亚分支，而另一菌株之一与来自牛源的鼠伤寒沙门氏菌分支。基于 DNA 序列的系统发育多样性分析表明，IncFIB 质粒编码的 Sit 和气杆菌素铁摄取系统在包括肠炎沙门氏菌在内的细菌物种中是保守的。通过接合将 IncFIB 质粒转移到肠炎沙门氏菌的 IncFIB 质粒缺陷菌株中。转接合子 SE819::IncFIB 在人肠上皮（Caco-2）细胞中的持续存在率高于受体 SE819。IncFIB 质粒中 Sit 和气杆菌素操纵子的基因在富铁和缺铁生长培养基中差异表达。
在不同细菌物种（包括食源性沙门氏菌菌株）中存在的 IncFIB 质粒中的 Sit 和气杆菌素操纵子中检测到最小的序列多样性。IncFIB 质粒编码的因子在宿主细胞的低铁条件下感染期间发挥作用。
