Role of metal transport in Streptococcus sanguinis virulence and competitiveness

 描述（由申请人提供）：感染性心内膜炎是一种严重的心脏感染，死亡率超过20%。这种疾病被认为是当细菌或其他微生物进入血液，附着在先前受损的心脏瓣膜上并繁殖时发生的。口腔链球菌或草绿色链球菌是导致这种疾病的主要原因，其中，血链球菌尤为重要。心内膜炎的预防主要依赖于在可能导致菌血症的牙科手术前对高危患者进行抗生素预防。然而，现在人们认识到，大多数心内膜炎病例是由于日常活动导致菌血症，牙科抗生素预防不能提供保护。毒力决定因素的鉴定可以为新的预防措施提供新的目标，这些措施能够为处于风险中的人提供持续的保护，而不会选择口腔中的抗生素耐药性。为了实现这一目标，我们进行了S.血吸虫突变体在动物模型中丧失心内膜炎毒力。这些研究已经确定了一种脂蛋白，SsaB，它对心内膜炎的毒力非常重要，也是一种有希望的治疗或预防靶点。SsaB，像它所属的家族的其他成员一样，在Mn（可能还有Fe）吸收，O2耐受性和毒性中发挥作用。有一些机制，锰可能有助于O2耐受性和毒力，但目前还不清楚究竟是采用或最重要的链球菌的机制。我们最近在SsaB的潜在功能方面取得了一些进展，这些功能不仅对S来说是新颖的。血链球菌，但对于任何链球菌，包括表征需氧生长所必需的Mn依赖性核糖核苷酸还原酶，表征ssaB突变体中剩余的超氧化物歧化酶活性的生物相关性，鉴定模拟兔心内膜炎模型结果的生理相关体外生长条件，观察SsaB蛋白的金属依赖性加工，以及SsaB在耐酸性中的重要作用的发现。我们建议通过检查SsaB的调节和功能来扩展这些新的发现。这将提供第一次测试在任何链球菌的多重假设所产生的我们最近的研究结果是有关金属运输。鉴于我们知道ssaB突变体的主要缺陷是代谢，我们研究的一个重要部分将是对在严格控制的条件下生长的O 2和酸应激细胞进行前所未有的代谢组学分析。随后将在口腔定植和心内膜炎毒力的体外和体内模型中测试选定的菌株，以测试我们发现的生物学相关性。这项研究的结果有望成为 直接适用于已知需要Mn的许多其它重要病原体和口腔定殖者。此外，这项研究有望确定新的方法来控制口腔健康和预防感染性心内膜炎。

 DESCRIPTION (provided by applicant): Infective endocarditis is a serious infection of the heart with mortality rates in excess of 20%. This disease is thought to occur when bacteria or other microbes gain access to the blood, attach to previously damaged heart valves, and multiply. The oral or viridans streptococci are a leading cause of this illness, and among this group, Streptococcus sanguinis is especially important. Prevention of endocarditis relies primarily on antibiotic prophylaxis for at-risk patients prior to dental procedures that are likelyto result in bacteremia. However, it is now recognized that most cases of endocarditis result from daily activities that lead to bacteremia, for which dental antibiotic prophylaxis provides no protection. The identification of virulence determinants could provide new targets for novel prophylactic measures capable of providing continuous protection for persons at risk without selecting for antibiotic resistance in the mouth. Toward this goal, we have performed multiple screens of S. sanguinis mutants for loss of endocarditis virulence in an animal model. These studies have identified a lipoprotein, SsaB, that is uniquely important for endocarditis virulence and is also a promising target for therapy or prevention. SsaB, like other members of the family to which it belongs, functions in Mn (and perhaps Fe) uptake, O2 tolerance, and virulence. There are a number of mechanisms by which Mn could contribute to O2 tolerance and virulence, but it is not clear exactly which mechanisms are employed or are most important in streptococci. We have made a number of recent advances in relation to SsaB's potential functions that are novel not just for S. sanguinis, but for any Streptococcus, including characterization of an Mn-dependent ribonucleotide reductase that is essential for aerobic growth, characterization of the biological relevance of superoxide dismutase activity remaining in an ssaB mutant, identifying physiologically relevant in vitro growth conditions that mimic findings from the rabbit endocarditis model, the observation of metal-dependent processing of the SsaB protein, and the finding of an important role for SsaB in acid tolerance. We propose to expand upon these novel findings by examining SsaB regulation and function. This will provide the first test in any Streptococcus of multiple hypotheses generated by our recent findings that are related to metal transport. Given that we know that the primary defect of an ssaB mutant is metabolic, an important part of our study will be an unprecedented metabolomic analysis of O 2 and acid-stressed cells grown under carefully controlled conditions. This will be followed by testing of selected strains in in vitro and in vivo models of oral colonization and endocarditis virulence to test the biological relevance of our findings. The results of this study promise to be directly applicable to a number of other important pathogens and oral colonizers that are known to require Mn. Moreover, this study promises to identify novel approaches to control oral health and prevent infective endocarditis.