ica phase variation in Staphylococcus epidermidis

描述（由申请人提供）：表皮葡萄球菌是涉及基于生物材料的器械的感染的主要原因。表皮葡萄球菌介导的异物感染发病机制中最重要的一步是生物体粘附并在生物材料表面产生生物膜的能力。在初始粘附后，某些表皮S菌株产生细胞外生物膜，或多糖细胞内粘附素（PIA），由四个基因（icaA, icaD， icaB和icaC）操纵子ica编码。在体外研究中，缺乏PIA生产的表皮葡萄球菌菌株的粘附性明显较低，在生物材料感染的体内模型中毒性较低。初步数据表明，PTA的产生受多层基因调控的支配。ica操纵子已被证明经历一种称为相位变化的现象，即一定比例的种群不产生PTA（生物膜阴性）。相变化被认为具有致病意义，因为那些不产生生物膜的细胞粘附性较差，可能会自由分散并定植到其他肥沃的地区，从而导致转移性疾病。本方案中提供的数据表明，至少有三类相位变化。I类变异可以被称为真正的“阶段变异”，因为它们很容易恢复到野生型（生物膜形成）。这些变异不产生可检测的ica转录本，但具有完整的ica操纵子。II类变异体产生很少的生物膜，可能是由于ica内的突变。III类变异由于丢失了包括ica在内的大基因组区域而不产生生物膜。本研究的主要目的是阐明PIA产生的遗传调控，并更好地表征假体装置感染发病机制中相位变化的重要性。该提案有四个具体目标：具体目标1：将定义负责ica转录调控的遗传位点，以及它们与I类期变异体中ica转录丢失机制的关系。具体目标2：将描述导致II类相变异的突变事件，并确定这些突变事件是随机的还是优先以有序的方式发生。具体目标3：将研究III类期变异，以确定在不同的表皮葡萄球菌菌株中切除位点是否保守。具体目的4：利用豚鼠组织笼模型和小鼠异物感染模型，确定相变异的致病意义。这一建议将为表皮葡萄球菌的发病机制和生物学的基本问题提供重要的新信息。这些研究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.