Role of phase-variable DNA methylase in virulence of Haemophilus influenzae

描述(申请人提供)：流感嗜血杆菌是人类鼻咽部正常菌群中的一员。它也是引起上呼吸道感染的原因，如中耳炎和支气管炎，以及全身感染，如菌血症和脑膜炎。理想情况下，预防或治疗流感嗜血杆菌疾病只会影响与疾病相关的细菌，而不会扰乱正常的菌群。这项工作的长期目标是了解从无症状的定植到粘膜或全身感染的转变。我们推测，鼻咽部细菌适应新环境(如中耳或血流)的机制之一是DNA甲基酶基因mod的相变。多年来，人们一直在研究流感嗜血杆菌外膜蛋白和脂多糖等表面结构的相变。Mod基因包含一个串联重复区域，与流感嗜血杆菌其他特征明确的相变基因相似，但mod相变的生理作用直到最近才为人所知。我们的合作者通过微阵列分析比较了mod缺失突变体和mod亲本，并报告了mod影响至少15个基因的转录(Srikhanta等人。2005 PNA 102：5547-51)显然是通过启动子的甲基化。不是所有这些基因都有已知的功能，但通常mod表达上调的基因与营养获取有关，而mod表达下调的基因中有几个属于热休克组。认为MOD的相变是一种随机的、协调的多个基因的开关机制。这些研究使用了实验室适应的无毒菌株RD KW20。在临床分离的流感嗜血杆菌和其他粘膜生物如脑膜炎奈瑟菌中也发现了阶段可变的mod基因。这个探索性项目将研究强毒流感嗜血杆菌的这种新的基因调控机制， (I)使用基因芯片识别临床分离株中与MOD相关的基因，以及 (Ii)研究MOD阶段在实验性感染中的作用。 发现MOD调控在临床分离株中普遍存在，并影响致病机制，这将为进一步研究细菌对人体内不同解剖生态位的生理适应提供基础。 流感嗜血杆菌是一种细菌，通常在人类喉咙中无害生长，但也能引起疾病。如果我们能够了解这些细菌在从喉咙移动到感染部位(如耳朵、肺部或血液)时是如何变化的，我们也许有一天能够预防疾病。

DESCRIPTION (provided by applicant): Haemophilus influenzae is a member of the normal bacterial flora colonizing the human nasopharynx. It is also a cause of infections of the upper respiratory tract, such as otitis media and bronchitis, and of systemic infections, such as bacteremia and meningitis. Ideally, prevention or treatment of H. influenzae disease would affect only disease-associated bacteria without perturbing normal flora. The long-term goal of this work is to understand the transition from asymptomatic colonization to mucosal or systemic infection. We hypothesize that one of the mechanisms by which nasopharyngeal bacteria adapt to a new environment such as the middle ear or the bloodstream is phase variation of a DNA methylase gene, mod. Phase variation of surface structures such as outer membrane proteins and lipopolysaccharide has been studied in H. influenzae for several years. The mod gene contains a tandem repeat region similar to those identified in other, well-characterized phase-variable genes in H. influenzae, but a physiologic role for mod phase variation was unknown until recently. Our collaborators compared a mod deletion mutant with a mod+ parent by microarray analysis and reported that mod affects transcription of at least 15 genes (Srikhanta et al. 2005 PNAS 102:5547-51) apparently via methylation of promoters. Not all of these genes have known functions, but generally genes upregulated by mod expression are involved in nutrient acquisition, while several of those downregulated by mod expression are in the heat-shock group. It is proposed that phase variation of mod is a mechanism for random, coordinated on/off switching of several other genes. These studies used the laboratory-adapted, avirulent strain Rd KW20. Phase-variable mod genes have also been identified in clinical isolates of H. influenzae and in other mucosal organisms such as Neisseria meningitidis. This exploratory project will study this novel mechanism of gene regulation in virulent H. influenzae, (i) using microarrays to identify mod-related genes in clinical isolates and (ii) examining the effect of mod phase in experimental infections. Finding that mod regulation is common in clinical isolates and affects pathogenesis will provide the basis for future studies on the physiological adaptation of bacteria to different anatomic niches within the human host. Haemophilus influenzae is a bacterium that usually grows harmlessly in the human throat, but is also able to cause disease. If we can understand how these bacteria change as they move from the throat to sites of infection (such as the ear, lungs, or blood), we may someday be able to prevent disease.