Understanding hypermucoviscosity in Klebsiella

摘要 肺炎克雷伯氏菌（Kpn）是革兰氏阴性菌医院感染的主要原因，并且与革兰氏阴性菌相关。 死亡率很高抗生素耐药性是肠杆菌科和肠杆菌属中日益严重的问题。 肠杆菌科Kpn是最常见的超广谱β-内酰胺酶和碳青霉烯类耐药菌 肠杆菌科分离株。耐药Kpn的日益流行只会加剧其 临床重要性和复杂的治疗选择。荚膜已被确立为关键毒力 因子，是该物种最好的研究毒力因子。Kpn菌株被广泛地分类为高毒力（hv） 或经典的，其中HV菌株通常引起社区获得性肝脓肿和侵入性感染。 经典菌株更典型地与医院感染相关。hv病毒株有一个 高粘（HMV）表型被认为是由于包膜过度产生并获得了rmpA 这有助于增加荚膜（CPS）基因表达。大多数经典菌株，包括最近的临床 与碳青霉烯耐药相关的分离株（ST 258）不是HMV，不具有rmpA基因， 在小鼠感染模型中具有毒性。最近的报告表明，这些多药耐药菌株获得了 HMV表型是一个重要的问题，并扩大了了解HMV是什么，它是如何发生的需要。 以及它是如何产生毒力的。尽管HMV与 包膜的过量产生，什么导致HMV表型及其与包膜的关系 生产情况不详。我们实验室最近使用HMV毒株KPPR 1 S的工作表明， rmpA导致cps启动子表达的减少，并且两种启动子的表达都减少（但不是完全丧失）。 胶囊生产和HMV。此外，我们发现rmpA是操纵子的第一个基因（rmpADC）， RmpA正调控操纵子的表达。分析完全删除的 操纵子与单个基因的同源性表明，从该基因座，RmpA主要是表达 操纵子，仅RmpC是cps基因表达所必需的，并且仅RmpD是HMV所必需的。 与此相一致，仅缺乏rmpD的突变体保留了cps基因表达、荚膜产生 HMV阴性。rmpD突变体是第一个鉴定出的将HMV与过表达的HMV分离的突变体。 生产的胶囊，和表型的菌株只表达rmpC表明，过度- 单独生产胶囊对于HMV是不够的。由于HMV对hv毒力的重要性， Kpn菌株，经典菌株获得HMV的潜力，构成HMV的不完整图片 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的相互作用伙伴以及它们如何影响HMV，并决定HMV的组成 外泌多糖，和（c）检查HMV如何有助于毒力。

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.