Helper Phage Mobilization of Staphylococcal Enterotoxin Genes

描述（由申请人提供）：金黄色葡萄球菌是一种危险的人类病原体，可导致社区获得性疾病和医院感染。金黄色葡萄球菌菌株由于产生多种毒素而引起各种疾病症状。对多种抗生素具有耐药性的菌株的出现，加上毒素基因的水平转移，构成了重大的公共卫生危害。大量的葡萄球菌超级抗原，包括肠毒素B、C和中毒性休克毒素，最近被证明编码在一个相关的15-20 kb致病性岛（SaPIs）家族上。SaPIs是一种新型的可移动遗传元件，可以在辅助噬菌体感染后高频转移。对原型元件SaPIs的研究表明，噬菌体诱导了致病性岛的切除和复制，随后将致病性岛包装成转导病毒粒子。SaP1转导颗粒与辅助噬菌体相似，但其头部的体积约为形成斑块的辅助噬菌体颗粒的1/3，与SaPH基因组的较小尺寸相称。SaPH的动员是非常高效的（比染色体标记的广义转导高6个数量级），迄今为止已经证明了对单个辅助噬菌体80 α的动员。第二个超抗原致病性岛SaPI2由葡萄球菌噬菌体80转导，其频率与SaPI1的80 α转导频率相似。噬菌体介导的这些致病性岛的切除、复制和封装的机制以及观察到的噬菌体特异性的决定因素仍有待阐明，这是该项目的长期目标。拟议的研究将在较小的SaPI转导颗粒中确定病毒粒子蛋白的身份和来源。研究人员将确定辅助噬菌体和SaPI基因参与SaPI小衣壳的形成，并研究SaPI编码的小端酶亚基在SaPI DNA包装中的作用。这些研究将提供洞察两个辅助遗传因素之间的显著关系，负责葡萄球菌肠毒素的传播。这一知识将有助于制定抑制金黄色葡萄球菌菌株之间毒素基因转移的策略，并有助于减缓高毒力、多重耐药生物的出现。

DESCRIPTION (provided by applicant): Staphylococcus aureus is a dangerous human pathogen responsible for both community acquired disease and nosocomial infections. S. aureus strains cause a variety of disease symptoms due to the production of a wide array of toxins. The emergence of strains resistant to multiple antibiotics, in combination with the horizontal transfer of toxin genes, poses a significant public health hazard. A large number of staphylococcal superantigens, including enterotoxins B, C and toxic shock toxin, have recently been shown to be encoded on a family of related, 15-20 kb pathogenicity islands (SaPIs). The SaPIs represent a novel type of mobile genetic element, which can be transferred at high frequency following helper phage infection. Studies of SaPIs, the prototype element, demonstrated phage-induced excision and replication of the pathogenicity island, followed by the packaging of the pathogenicity island into transducing virions. SaP1 transducing particles resemble those of the helper phage but have heads about 1/3 the volume of the plaque-forming helper phage particles, commensurate with the smaller size of the SaPH genome. SaPH mobilization is highly efficient (about 6 orders of magnitude higher than generalized transduction of chromosomal markers), and thus far has been demonstrated for a single helper phage, 80 alpha. A second superantigen pathogenicity island, SaPI2, is transduced by staphylococcal phage 80 at a frequency similar to that seen for SaPI1 with 80 alpha. The mechanisms underlying the phage-mediated excision, replication and encapsidation of these pathogenicity islands as well as the determinants of the observed phage specificity remain to be elucidated, and represent the long-term goal of this project. The proposed studies will establish the identity and origin of the virion proteins in the smaller SaPI transducing particles. Helper phage and SaPI genes involved in formation of the smaller SaPI capsids will be determined, and the role of a SaPI-encoded small terminase subunit in SaPI DNA packaging will be investigated. These studies will provide insight into the remarkable relationship between two accessory genetic elements that are responsible for the dissemination of staphylococcal enterotoxins. This knowledge will assist in the development of strategies to inhibit the transfer of toxin genes between Staphylococcus aureus strains and help slow the emergence of highly virulent, multiresistant organisms.