Mechanisms of Staphylococcal Co-Resistance to Daptomycin and Host Defense Peptide

描述(申请人提供)：金黄色葡萄球菌(SA)引起广泛的临床症状，是世界范围内血管内感染的主要原因。沙门氏菌具有产生多重耐药性的特殊倾向，严重感染此类菌株会导致归因性死亡率增加。自2003年FDA批准以来，达托霉素(DAP)已在许多临床环境中使用，特别是对耐甲氧西林金黄色葡萄球菌(MRSA)感染的治疗。最近有许多报道称，在DAP治疗方案失败的情况下，尤其是在血管内感染的情况下，临床SA菌株在体外进化出对DAP的耐药性。DAP-R菌株的一个一贯特征是在相对受限的一组基因中获得一个或多个“功能增益”突变，特别是mprF(多肽耐药因子基因)。该基因负责SA特有的、带正电荷的磷脂(PL)、赖氨酰磷脂酰甘油(L-PG)在细胞膜(CM)内的合成和转位(“翻转”)。因此，mprF对SA的相对正表面电荷有很大贡献。此外，鉴于DAP的细菌致死性绝对需要钙缔合，影响表面电荷的mprF等基因很可能在DAP-R中非常重要，可能是通过电荷排斥。临床和体外来源的DAP-R SA株的一个基本特征是DAP和阳离子宿主防御肽(HDPs)(13，15，17-19)之间频繁的交叉耐药。因此，我们的中心假设是，DAP-R在MRSA中的发展经常与HDP耐药的共同进化相关，并且这一事件影响血管内发病机制和体内治疗结果。我们将解决一些重要的问题：i)mprF功能增益突变多久伴随DAP-HDP交叉耐药表型？ii)这种mprF突变是否偏向于该基因的合成酶或翻转酶结构域，它们是导致交叉耐药的原因吗？iii)在那些表现出DAP-HDP交叉耐药表型的多肽中是否存在HDP特有的结构特征？iv)金黄色葡萄球菌菌株对DAP和/或HDP的时间暴露“时间表”是否影响交叉耐药的发展？和vi)mprF突变和DAP-HDP交叉耐药对先天毒力和对DAP治疗的反应在体内的后果是什么？我们预计这些研究将有助于更深入地了解我们的固有宿主防御系统与外源性抗菌素在刺激SA适应性生存反应中的交互作用。这将使未来新型抗金黄色葡萄球菌药物的“智能设计”能够绕过这种适应性反应。

DESCRIPTION (provided by applicant): S. aureus (SA) causes a wide spectrum of clinical syndromes, and is the leading cause of endovascular infections world-wide. SA has a particular propensity to develop multi-drug resistance, and serious infections with such strains result in enhanced attributable mortalities. Since FDA approval in 2003, daptomycin (DAP) has been utilized in many clinical settings, especially for recalcitrant methicillin-resistant SA (MRSA) infections. There have been numerous recent reports of clinical SA strains that have evolved in vitro DAP-resistance in the context of failing DAP treatment regimens, especially in endovascular infections. One consistent feature of DAP-R strains is the acquisition of one or more "gain-in-function" mutations in a relatively restricted cadre of genes, especially mprF (multiple peptide resistance factor gene). This gene is responsible for the synthesis and translocation ("flipping") of the SA-unique, positively-charged phospholipid (PL), lysyl-phosphotidylglycerol (L-PG) within its cell membrane (CM). Thus, mprF contributes substantially to the relative positive surface charge of SA. Moreover, in light of the absolute requirement for calcium association for DAP's bacterial lethality, genes such as mprF that impact surface charge are highly likely to be important in DAP-R, potentially via charge repulsion. A seminal feature of both clinical and in vitro-derived DAP-R SA strains is the frequent cross-resistance between DAP and cationic host defense peptides (HDPs) (13,15,17-19). Thus, our central hypothesis is that the development of DAP- R in MRSA is frequently associated with the co-evolution of HDP resistance, and this event impacts endovascular pathogenesis and treatment outcomes in vivo. We will address a number of important questions: i) how often do mprF gain-in-function mutations accompany DAP-HDP cross-resistance phenotypes?; ii) are such mprF mutations biased towards the synthase or flippase domains of this gene, and are they causal in cross-resistance?; iii) are there HDP- specific structural features that are shared amongst those peptides which exhibit the DAP-HDP cross-resistance phenotype?; iv) does the temporal exposure "schedule" of S. aureus strains to DAP and/or HDPs influence the development of cross-resistance?; and vi) what are the in vivo consequences of mprF mutations and DAP-HDP cross resistances upon innate virulence and responses to DAP therapy? We anticipate that these studies will contribute to a deeper understanding of the interactive role of our innate host defense system with exogenously administered antimicrobials in stimulating the adaptive survival response in SA. This should enable 'smart design' of future novel anti-SA agents that circumvent this adaptive response.