Klughammer Johanna, Dittrich Marcus, Blom Jochen, Mitesser Vera, Vogel Ulrich, Frosch Matthias, Goesmann Alexander, Müller Tobias, Schoen Christoph
CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.
Institute for Hygiene and Microbiology, University of Würzburg, Würzburg, Germany.
PLoS One. 2017 Jan 12;12(1):e0169892. doi: 10.1371/journal.pone.0169892. eCollection 2017.
Some members of the physiological human microbiome occasionally cause life-threatening disease even in immunocompetent individuals. A prime example of such a commensal pathogen is Neisseria meningitidis, which normally resides in the human nasopharynx but is also a leading cause of sepsis and epidemic meningitis. Using N. meningitidis as model organism, we tested the hypothesis that virulence of commensal pathogens is a consequence of within host evolution and selection of invasive variants due to mutations at contingency genes, a mechanism called phase variation. In line with the hypothesis that phase variation evolved as an adaptation to colonize diverse hosts, computational comparisons of all 27 to date completely sequenced and annotated meningococcal genomes retrieved from public databases showed that contingency genes are indeed enriched for genes involved in host interactions. To assess within-host genetic changes in meningococci, we further used ultra-deep whole-genome sequencing of throat-blood strain pairs isolated from four patients suffering from invasive meningococcal disease. We detected up to three mutations per strain pair, affecting predominantly contingency genes involved in type IV pilus biogenesis. However, there was not a single (set) of mutation(s) that could invariably be found in all four pairs of strains. Phenotypic assays further showed that these genetic changes were generally not associated with increased serum resistance, higher fitness in human blood ex vivo or differences in the interaction with human epithelial and endothelial cells in vitro. In conclusion, we hypothesize that virulence of meningococci results from accidental emergence of invasive variants during carriage and without within host evolution of invasive phenotypes during disease progression in vivo.
生理性人类微生物群的一些成员偶尔会引发危及生命的疾病，即使在免疫功能正常的个体中也是如此。这类共生病原体的一个典型例子是脑膜炎奈瑟菌，它通常寄居于人类鼻咽部，但也是败血症和流行性脑膜炎的主要病因。以脑膜炎奈瑟菌作为模式生物，我们检验了这样一个假说：共生病原体的毒力是宿主内进化以及因应急基因发生突变而选择侵袭性变体的结果，这一机制称为相变。与相变作为一种适应不同宿主定殖方式而进化的假说相符，从公共数据库检索到的所有27个已完成全测序和注释的脑膜炎球菌基因组的计算比较表明，应急基因确实富含参与宿主相互作用的基因。为了评估脑膜炎球菌在宿主体内的基因变化，我们进一步对从4名侵袭性脑膜炎球菌病患者分离出的咽喉-血液菌株对进行了超深度全基因组测序。我们在每对菌株中检测到多达3个突变，主要影响参与IV型菌毛生物合成的应急基因。然而，在所有4对菌株中并非总能找到单一（组）突变。表型分析进一步表明，这些基因变化通常与血清抗性增加、在人血中的体外适应性提高或与人类上皮细胞和内皮细胞体外相互作用的差异无关。总之，我们推测脑膜炎球菌的毒力源于携带期间侵袭性变体的偶然出现，而非体内疾病进展过程中侵袭性表型的宿主内进化。
