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Abstract：
Streptococcus agalactiae causes sepsis and meningitis in neonates, presenting substantial clinical challenges. Type VII secretion system (T7SS), an important secretion system identified in Mycobacterium sp. and Gram-positive bacteria, was recently characterized in S. agalactiae and considered to contribute to its virulence and pathogenesis. In the present study, 128 complete genomic sequences of S. agalactiae were retrieved from GenBank to build a public dataset, and their sequences, capsular types, and clonal complexes were determined. Polymerase chain reaction (PCR) screening and genomic sequencing were conducted in an additional clinical dataset. STs and capsular types were determined using PCR. Eleven different types of T7SS were detected with similarities in gene order but differences in gene content. Strains with incomplete T7SS or lack of T7SS were also identified. Deletion, insertion, and segmentation of T7SS might be related to insertion sequences. The genetic environment of T7SS in S. agalactiae was also investigated and different patterns were identified downstream the T7SS, which were related to the diversity of T7SS putative effectors. The T7SS demonstrated possible sequence type (ST)-dependent diversity in both datasets. This work elucidated detailed genetic characteristics of T7SS and its genetic environment in S. agalactiae and further identified its possible ST-dependent diversity, which gave a clue of its mode of transmission. Further investigations are required to elucidate the underlying mechanisms and its functions.
摘要：
无乳链球菌导致新生儿败血症和脑膜炎，提出了重大的临床挑战。VII型分泌系统（T7SS），分枝杆菌中鉴定出的重要分泌系统。和革兰氏阳性菌,最近在无乳链球菌中表征，并被认为有助于其毒力和发病机理。在本研究中,从GenBank检索到128个完整的无乳链球菌基因组序列，以建立一个公共数据集，和它们的序列，囊膜类型，并确定了克隆复合物。在另外的临床数据集中进行聚合酶链反应(PCR)筛选和基因组测序。使用PCR确定STs和荚膜类型。检测到11种不同类型的T7SS，基因顺序相似，但基因含量不同。还鉴定了具有不完全T7SS或缺乏T7SS的菌株。删除,插入,T7SS的分段可能与插入序列有关。还研究了无乳链球菌中T7SS的遗传环境，并在T7SS下游鉴定了不同的模式。这与T7SS推定效应子的多样性有关。T7SS在两个数据集中证明了可能的序列类型(ST)依赖性多样性。这项工作阐明了T7SS的详细遗传特征及其在无乳链球菌中的遗传环境，并进一步确定了其可能的ST依赖性多样性。这给出了它的传播方式的线索。需要进一步调查以阐明潜在的机制及其功能。
