ica phase variation in Staphylococcus epidermidis

描述（由申请人提供）：表皮葡萄球菌是生物材料器械感染的主要原因。S.表皮介导的异物感染是生物体在生物材料表面粘附和产生生物膜的能力。在初始粘附后，某些表皮葡萄球菌菌株产生细胞外生物膜或多糖细胞内粘附素（PIA），其由四个基因（icaA、icaD、icaB和icaC）操纵子伊卡编码。链球菌菌株在体外研究中，PIA产生缺陷的表皮葡萄球菌的粘附性明显较低，并且在基于生物材料的感染的体内模型中毒性较低。初步数据表明，PTA生产是由多层基因调控。伊卡操纵子已经显示出经历称为相位变化的现象，其中一定比例的群体不产生PTA（生物膜阴性）。已经假设相位变化具有致病性意义，因为不产生生物膜的那些细胞粘附性较低，并且可以自由分散和定殖于其他可繁殖区域，从而导致转移性疾病。本提案中提供的数据表明，至少有三类相位变体。I类变体可以被称为真正的“相变体”，因为它们容易恢复为野生型（生物膜形成）。这些变体不产生可检测的伊卡转录本，但具有完整的伊卡操纵子。II类变异体产生的生物膜很少，可能是由于伊卡内的突变。III类变体由于包括伊卡的大基因组区域的丢失而不产生生物膜。本研究的主要目的是阐明PIA产生的遗传调控，并更好地表征相位变化在假体器械感染发病机制中的重要性。该提案有四个具体目标：具体目标1：将定义负责伊卡转录调控的遗传基因座，以及它们与I类相位变体中伊卡转录丧失机制的关系。具体目标2：将表征导致II类相位变体的突变事件，并确定这些突变事件是随机的还是优先以有序方式发生。具体目标3：将研究III类相变异体，以确定切除位点在不同的链球菌菌株中是否保守。表皮具体目标4：将使用豚鼠组织笼模型和小鼠异物感染模型来确定相变体的致病意义。这一建议将产生重要的新信息的基本问题的S。表皮病发病机制和生物学。作为这些研究的结果，可能会提出预防和治疗基于生物材料的感染的新方法。

DESCRIPTION (provided by applicant): Staphylococcus epidermidis is the preeminent cause of infections involving biomaterial-based devices. The most important step in the pathogenesis of S. epidermidis mediated foreign body infections is the ability of the organism to adhere and to produce biofilm on the surface of the biomaterial. After initial adherence, certain strains of S epidermidis produce an extracellular biofilm, or polysaccharide intracellular adhesin (PIA), that is encoded by a four gene (icaA, icaD, icaB, and icaC) operon ica. Strains of S. epidermidis deficient in the production of PIA are significantly less adherent in in vitro studies and are less virulent in in vivo models of biomaterial based infections. Preliminary data suggest that PTA production is governed by multiple layers of gene regulation. The ica operon has been shown to undergo a phenomenon termed phase variation, whereby a certain proportion of the population do not produce PTA (biofilm-negative). Phase variation has been hypothesized to have pathogenic significance in that those cells not producing biofilm are less adherent and may be free to disperse and colonize other fertile areas resulting in metastatic disease. Data presented in this proposal demonstrate that there are at least three classes of phase variants. Class I variants can be termed true "phase variants" as they readily revert to wild-type (biofilm forming). These variants do not produce detectable ica transcript yet have an intact ica operon. Class II variants produce little biofilm presumably due to mutations within ica. Class III variants do not produce biofilm due to the loss of a large genomic region which includes ica. The major goal of this study is to elucidate the genetic regulation of PIA production and better characterize the importance of phase variation in the pathogenesis of prosthetic device infection. This proposal has four specific aims: Specific aim 1: Genetic loci that are responsible for regulation of ica transcription, and their relationship to the mechanism governing loss of ica transcription in class I phase variants, will be defined. Specific aim 2: Mutational events responsible for class II phase variants will be characterized and it will be determined whether these mutational events are random or whether they preferentially occur in an ordered manner. Specific aim 3: Class III phase variants will be studied in order to ascertain whether the excision site is conserved amongst different strains of S. epidermidis. Specific aim 4: A guinea pig tissue cage model and mouse foreign body infection model will be utilized to ascertain the pathogenic significance of phase variants. This proposal will yield significant new information regarding fundamental questions of S. epidermidis pathogenesis and biology. Novel means to prevent and treat biomaterial-based infections may be suggested as a result of these studies.