Laboratory of Pediatric Infectious Diseases, Radboud University Medical Centre, Nijmegen, Netherlands.
mBio. 2012 Jul 3;3(4):e00079-12. doi: 10.1128/mBio.00079-12. Print 2012.
Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative, human-restricted pathogen. Although this bacterium typically colonizes the nasopharynx in the absence of clinical symptoms, it is also one of the major pathogens causing otitis media (OM) in children. Complement represents an important aspect of the host defense against NTHi. In general, NTHi is efficiently killed by complement-mediated killing; however, various resistance mechanisms have also evolved. We measured the complement resistance of NTHi isolates isolated from the nasopharynx and the middle ear fluids of OM patients. Furthermore, we determined the molecular mechanism of NTHi complement resistance. Complement resistance was strongly increased in isolates from the middle ear, which correlated with decreased binding of IgM. We identified a crucial role for the R2866_0112 gene in complement resistance. Deletion of this gene altered the lipooligosaccharide (LOS) composition of the bacterium, which increased IgM binding and complement-mediated lysis. In a novel mouse model of coinfection with influenza virus, we demonstrate decreased virulence for the R2866_0112 deletion mutant. These findings identify a mechanism by which NTHi modifies its LOS structure to prevent recognition by IgM and activation of complement. Importantly, this mechanism plays a crucial role in the ability of NTHi to cause OM.
Nontypeable Haemophilus influenzae (NTHi) colonizes the nasopharynx of especially young children without any obvious symptoms. However, NTHi is also a major pathogen in otitis media (OM), one of the most common childhood infections. Although this pathogen is often associated with OM, the mechanism by which this bacterium is able to cause OM is largely unknown. Our study addresses a key biological question that is highly relevant for child health: what is the molecular mechanism that enables NTHi to cause OM? We show that isolates collected from the middle ear fluid exhibit increased complement resistance and that the lipooligosaccharide (LOS) structure determines IgM binding and complement activation. Modification of the LOS structure decreased NTHi virulence in a novel NTHi-influenza A virus coinfection OM mouse model. Our findings may also have important implications for other Gram-negative pathogens harboring LOS, such as Neisseria meningitidis, Moraxella catarrhalis, and Bordetella pertussis.
未分型流感嗜血杆菌（NTHi）是一种革兰氏阴性、人类局限的病原体。尽管这种细菌通常在没有临床症状的情况下定植于鼻咽部，但它也是导致儿童中耳炎（OM）的主要病原体之一。补体是宿主防御 NTHi 的一个重要方面。一般来说，NTHi 可被补体介导的杀伤有效杀灭；然而，各种耐药机制也已经进化出来。我们测量了从 OM 患者鼻咽部和中耳液中分离的 NTHi 分离株的补体耐药性。此外，我们还确定了 NTHi 补体耐药性的分子机制。中耳分离株的补体耐药性显著增强，这与 IgM 结合减少有关。我们发现 R2866_0112 基因在补体耐药性中起着关键作用。该基因的缺失改变了细菌的脂寡糖（LOS）组成，增加了 IgM 结合和补体介导的裂解。在新型流感病毒共感染的小鼠模型中，我们证明 R2866_0112 缺失突变体的毒力降低。这些发现确定了 NTHi 修饰其 LOS 结构以防止 IgM 识别和补体激活的机制。重要的是，这种机制在 NTHi 引起 OM 的能力中起着至关重要的作用。
