Genomic, Transcriptomic, and Phenotypic Analyses of Neisseria meningitidis Isolates from Disease Patients and Their Household Contacts

<i>Neisseria meningitidi</i>s (meningococcus) can cause meningococcal disease, a rapidly progressing and often fatal disease that can occur in previously healthy children. Meningococci are found in healthy carriers, where they reside in the nasopharynx as commensals. While carriage is relatively common, invasive disease, associated with hypervirulent strains, is a comparatively rare event. The basis of increased virulence in some strains is not well understood. New Zealand suffered a protracted meningococcal disease epidemic, from 1991 to 2008. During this time, a household carriage study was carried out in Auckland: household contacts of index meningococcal disease patients were swabbed for isolation of carriage strains. In many households, healthy carriers harbored strains identical, as determined by laboratory typing, to the ones infecting the associated patient. We carried out moredetailed analyses of carriage and disease isolates from a select number of households. We found that isolates, although indistinguishable by laboratory typing methods and likely closely related, had many differences. We identified multiple genome variants and transcriptional differences between isolates. These studies enabled the identification of two new phase-variable genes. We also found that several carriage strains had lost their type IV pili and that this loss correlated with reduced tumor necrosis factor alpha (TNF-alpha) expression when cultured with epithelial cells. While nonpiliated meningococcal isolates have been previously found in carriage strains, this is the first evidence of an association between type IV pili from meningococci and a proinflammatory epithelial response. We also identified potentially important metabolic differences between carriage and disease isolates, including the sulfate assimilation pathway.<br><b>IMPORTANCE:</b> <i>Neisseria meningitidis</i> causes meningococcal disease but is frequently carried in the throats of healthy individuals; the factors that determine whether invasive disease develops are not completely understood. We carried out detailed studies of isolates, collected from patients and their household contacts, to identify differences between commensal throat isolates and those that caused invasive disease. Though isolates were identical by laboratory typing methods, we uncovered many differences in their genomes, in gene expression, and in their interactions with host cells. In particular, we found that several carriage isolates had lost their type IV pili, a surprising finding since pili are often described as essential for colonization. However, loss of type IV pili correlated with reduced secretion of a proinflammatory cytokine, TNF-alpha, when meningococci were cocultured with human bronchial epithelial cells; hence, the loss of pili could provide an advantage to meningococci, by resulting in a dampened localized host immune response.

脑膜炎奈瑟菌（Neisseria meningitidis，俗称脑膜炎球菌）可引发脑膜炎球菌病，这是一种进展迅速且常可致命的疾病，甚至可感染既往健康的儿童。脑膜炎球菌常定植于健康携带者的鼻咽部，作为共生菌存在。尽管带菌状态较为普遍，但与高毒力菌株相关的侵袭性疾病却相对罕见。部分菌株毒力增强的分子机制目前仍未完全阐明。
新西兰在1991年至2008年间经历了一场持续多年的脑膜炎球菌病流行。在此期间，研究团队在奥克兰开展了一项家庭带菌状况研究：对脑膜炎球菌病先证者的家庭接触者进行鼻咽拭子采样，以分离带菌菌株。在多数家庭中，经实验室分型鉴定，健康携带者携带的菌株与感染对应先证者的菌株完全一致。
研究团队对选取的若干家庭的带菌菌株和致病菌株开展了更细致的分析。结果发现，尽管这些分离株经实验室分型方法无法区分且亲缘关系密切，但二者存在诸多差异。研究团队鉴定出分离株之间存在多种基因组变异和转录水平差异。本研究还发现了两个新的相位可变基因（phase-variable genes）。此外，研究团队发现部分带菌菌株丢失了IV型菌毛（type IV pili），且该丢失现象与上皮细胞共培养时肿瘤坏死因子α（TNF-α）的表达下调相关。尽管此前已有研究在带菌菌株中发现无IV型菌毛的脑膜炎奈瑟菌分离株，但本研究首次证实脑膜炎奈瑟菌的IV型菌毛与促炎性上皮细胞应答之间存在关联。研究团队还鉴定出带菌菌株与致病菌株之间存在潜在关键的代谢差异，其中包括硫酸盐同化途径（sulfate assimilation pathway）。
【研究意义】
脑膜炎奈瑟菌（Neisseria meningitidis）可引发脑膜炎球菌病，同时也常定植于健康人群的咽部，但目前尚未完全明确决定其引发侵袭性疾病的关键因素。研究团队对从患者及其家庭接触者中采集的分离株开展了细致研究，以区分共生性咽部定植菌株与致病菌株之间的差异。尽管这些分离株经实验室分型方法无法区分，但研究团队发现二者在基因组、基因表达以及与宿主细胞的相互作用方面均存在诸多差异。尤为值得关注的是，研究团队发现部分带菌分离株丢失了IV型菌毛——这一发现颇为出人意料，因为通常认为菌毛是定植所必需的结构。然而，当脑膜炎奈瑟菌与人类支气管上皮细胞共培养时，IV型菌毛的丢失与促炎性细胞因子TNF-α的分泌减少相关。因此，菌毛的丢失可能通过减弱局部宿主免疫应答，为脑膜炎奈瑟菌提供生存优势。