Institute of Veterinary Bacteriology, Vetsuisse, University of Bern, Bern, Switzerland.
Dean's Office, Vetsuisse Faculty, University of Bern, Bern, Switzerland.
Infect Genet Evol. 2018 Oct;64:115-125. doi: 10.1016/j.meegid.2018.06.024. Epub 2018 Jun 20.
Bacillus anthracis, the etiological agent of anthrax, procures its particular virulence by a capsule and two AB type toxins: the lethal factor LF and the edema factor EF. These toxins primarily disable immune cells. Both toxins are translocated to the host cell by the adhesin-internalin subunit called protective antigen PA. PA enables LF to reach intra-luminal vesicles, where it remains active for long periods. Subsequently, LF translocates to non-infected cells, leading to inefficient late therapy of anthrax. B. anthracis undergoes slow evolution because it alternates between vegetative and long spore phases. Full genome sequence analysis of a large number of worldwide strains resulted in a robust evolutionary reconstruction of this bacterium, showing that B. anthracis is split in three main clades: A, B and C. Clade A efficiently disseminated worldwide underpinned by human activities including heavy intercontinental trade of goat and sheep hair. Subclade A.Br.WNA, which is widespread in the Northern American continent, is estimated to have split from clade A reaching the Northern American continent in the late Pleistocene epoch via the former Bering Land Bridge and further spread from Northwest southwards. An alternative hypothesis is that subclade A.Br.WNA. evolved from clade A.Br.TEA tracing it back to strains from Northern France that were assumingly dispatched by European explorers that settled along the St. Lawrence River. Clade B established mostly in Europe along the alpine axis where it evolved in association with local cattle breeds and hence displays specific geographic subclusters. Sequencing technologies are also used for forensic applications to trace unintended or criminal acts of release of B. anthracis. Under natural conditions, B. anthracis generally affects domesticated and wild ruminants in arid ecosystems. The more recently discovered B. cereus biovar anthracis spreads in tropical forests, where it threatens particularly endangered primate populations.
炭疽杆菌是炭疽病的病原体，通过荚膜和两种 AB 型毒素：致死因子 LF 和水肿因子 EF 获得其特殊的毒力。这些毒素主要使免疫细胞失能。两种毒素都通过称为保护性抗原 PA 的黏附素-内毒素亚单位被转运到宿主细胞中。PA 使 LF 到达腔内腔泡，在那里它保持长时间的活性。随后，LF 转运到未感染的细胞，导致炭疽病的后期治疗效果不佳。炭疽杆菌经历缓慢的进化，因为它在营养体和长孢子阶段之间交替。对大量来自世界各地的菌株的全基因组序列分析导致对该细菌进行了强有力的进化重建，表明炭疽杆菌分为三个主要分支：A、B 和 C。分支 A 通过包括山羊和绵羊毛发的洲际贸易在内的人类活动在全球范围内有效地传播。广泛分布在北美大陆的亚分支 A.Br.WNA 估计是从分支 A 中分离出来的，在更新世晚期通过以前的白令陆桥到达北美大陆，并从西北向南进一步传播。另一种假设是，亚分支 A.Br.WNA 是从分支 A.Br.TEA 进化而来的，可以追溯到来自法国北部的菌株，这些菌株可能是由在圣劳伦斯河沿岸定居的欧洲探险家派遣的。分支 B 主要在欧洲沿阿尔卑斯山脉建立，与当地牛种一起进化，因此显示出特定的地理亚群。测序技术也用于法医应用，以追踪炭疽杆菌的非故意或犯罪释放行为。在自然条件下，炭疽杆菌通常影响干旱生态系统中的家养和野生反刍动物。最近发现的炭疽芽孢杆菌 B. cereus 生物变种在热带森林中传播，对特别濒危的灵长类动物种群构成威胁。
