Understanding hypermucoviscosity in Klebsiella

摘要 肺炎克雷伯菌(Kpn)是革兰氏阴性菌医院感染的主要原因，与 死亡率很高。抗生素耐药性在肠杆菌科和肠杆菌科中是一个日益严重的问题 肠杆菌科最常见的超广谱β-内酰胺酶和碳青霉烯类耐药 肠杆菌科分离株。耐药KPN的日益流行只会使其复杂化 临床重要性，并使治疗选择复杂化。胶囊已被确定为一种关键的毒力 因子，是该物种研究最多的毒力因子。Kpn毒株被广泛归类为超强毒力(Hv)。 或者是经典的，典型的Hv毒株会导致社区获得性肝脓肿和侵袭性感染。 经典菌株更典型地与医院感染有关。Hv病毒株有一种 高粘滞性(HMV)表型被认为是由于胶囊的过度生产，并已获得rmpA 这有助于增加胶囊(Cps)基因的表达。大多数经典菌株，包括最近的临床 与碳青霉烯类耐药相关的分离株(ST258)不是HMV，没有rmpA基因，也不是 在感染的小鼠模型中具有致病性。最近有报道称这些耐多药菌株获得了 HMV的表型非常令人关注，并扩大了理解HMV是什么，它是如何发生的需要 以及它是如何导致毒性的。尽管HMV和HMV之间存在明显的联系 包膜过度生产、HMV表型的原因及其与包膜的关系 产量尚不清楚。我们实验室最近使用HMV毒株KPPR1S所做的工作表明， RmpA导致cps启动子的表达减少，并且两者都减少(但不是完全丧失) 胶囊生产和HMV。此外，我们还发现rmpA是操纵子(RmpADC)的第一个基因，并且 RmpA正向调节操纵子的表达。对完全删除 操纵子与单个基因的关系表明，在该基因座上，RmpA主要是表达 CPS基因的表达只需要RmpC，HMV只需要RmpD。 与此一致的是，仅缺乏rmpD的突变体保持了cps基因表达的wt水平，即胶囊生产 HMV阴性。RmpD突变体是第一个将HMV与Over-Go分离的突变体。 只表达rmpC的菌株的表型表明，过量表达rmpC。 仅生产胶囊是不足以制造HMV的。由于HMV对HV毒力的重要性 KPN毒株，经典毒株感染HMV的可能性，构成HMV的不完整图景 以及产生HMV所需的条件，我们建议a)更好地了解RmpD，(B)表征 RmpD的相互作用伙伴及其对HMV的影响，并决定HMV的组成 以及(C)研究HMV如何对毒力起作用。

Abstract Klebsiella pneumoniae (Kpn) is a leading cause of Gram-negative nosocomial infections and is associated with a high mortality rate. Antibiotic resistance is a growing issue among the Enterobacteriaceae and of the Enterobacteriaceae Kpn is the most prevalent extended spectrum β-lactamase and carbapenem resistant Enterobacteriaceae isolate. The increasing prevalence of antibiotic-resistant Kpn only serves to compound its clinical importance and to complicate treatment options. Capsule has been established as a key virulence factor and is this species best studied virulence factor. Kpn strains are broadly classified as hypervirulent (hv) or classical, with hv strains typically causing community acquired liver abscess and invasive infections. Classical strains are more typically associated with nosocomial infections. The hv strains have a hypermucoviscous (HMV) phenotype thought to be due to over-production of capsule and have acquired rmpA that contributes to increased capsule (cps) gene expression. Most classical strains, including recent clinical isolates associated with carbapenem resistance (ST258) are not HMV, do not have the rmpA gene and are not virulent in mouse models of infection. Recent reports of these multidrug resistant strains acquiring the HMV phenotype is of significant concern and amplifies the need to understand what HMV is, how it is produced and how it contributes to virulence. Despite the apparent association between HMV and over-production of capsule, what causes the HMV phenotype and its relationship to capsule production is not known. Recent work from our lab using the HMV strain KPPR1S has shown that deletion of rmpA causes decreases in expression from cps promoters, and reduction (but not complete loss) in both capsule production and HMV. In addition, we found that rmpA is the first gene of an operon (rmpADC) and that RmpA positively regulates expression of the operon. Results from analysis of a complete deletion of the operon with the individual genes indicates that from this locus, RmpA primarily is required for expression of the operon, that only RmpC is necessary for expression of cps genes, and that only RmpD is necessary for HMV. Consistent with this, a mutant lacking only rmpD retains WT levels of cps gene expression, capsule production and is HMV negative. The rmpD mutant is the first mutant identified that separates HMV from the over- production of capsule, and the phenotype of the strain only expressing rmpC indicates that over- production of capsule alone is not sufficient for HMV. Due to the importance of HMV to the virulence of hv Kpn strains, the potential for classical strains to acquire HMV, the incomplete picture of what constitutes HMV and what is required to produce HMV, we propose to a) gain a better understanding of RmpD, (b) characterize the interacting partners of RmpD and how they affect HMV, and determine the composition of the HMV exopolysaccharide, and (c) examine how HMV contributes to virulence.