Sullam P M, Bayer A S, Foss W M, Cheung A L
Department of Medicine, Veterans Affairs Medical Center and University of California, San Francisco 94121, USA.
Infect Immun. 1996 Dec;64(12):4915-21. doi: 10.1128/iai.64.12.4915-4921.1996.
The direct binding of platelets by bacteria is a postulated central mechanism in the pathogenesis of endocarditis. To address the role of binding more definitively, we employed Tn551 insertional mutagenesis of Staphylococcus aureus parental strain ISP479 to generate an isogenic variant (strain PS12) that bound platelets minimally. As compared with the binding of ISP479, the binding of PS12 to platelet monolayers was reduced by 67.2%. Similarly, the binding of PS12 to platelets in suspension was reduced by 71.3%, as measured by flow cytometry. The low-binding phenotype was transducible into both ISP479 and S. aureus Newman. Southern blotting indicated that a single copy of Tn551 was inserted within the chromosomes of PS12 and the transductants. When tested in a rabbit model, animals inoculated with PS12 were significantly less likely to develop endocarditis and had lower densities of organisms (CFU per gram) within vegetations and a decreased incidence of renal abscess formation, as compared with animals inoculated with the parental strain. The diminished virulence of PS12 was not attributable to a reduction in the initial attachment of organisms to the damaged endocardium, since 30 min after inoculation, PS12-infected animals had microbial densities on the valve surface comparable to those seen with the parental strain. These results indicate that the direct binding of Staphylococcus aureus to platelets is a major determinant of virulence in the pathogenesis of endocarditis. Staphylococcus-platelet binding appears to be critical for pathogenetic events occurring after the initial colonization of the valve surface, such as vegetation formation and septic embolization.
细菌与血小板的直接结合被认为是心内膜炎发病机制中的核心机制。为了更确切地阐明结合作用的角色，我们利用金黄色葡萄球菌亲本菌株ISP479进行Tn551插入诱变，以产生一个与血小板结合极少的同基因变体（菌株PS12）。与ISP479的结合相比，PS12与血小板单层的结合减少了67.2%。同样，通过流式细胞术检测，PS12与悬浮血小板的结合减少了71.3%。低结合表型可转导至ISP479和金黄色葡萄球菌纽曼菌株。Southern印迹法表明，Tn551的单拷贝插入到了PS12及转导子的染色体中。在兔模型中进行测试时，与接种亲本菌株的动物相比，接种PS12的动物发生心内膜炎的可能性显著降低，赘生物内的生物体密度（每克菌落形成单位）更低，肾脓肿形成的发生率也降低。PS12毒力减弱并非归因于生物体对受损心内膜初始黏附的减少，因为接种后30分钟，感染PS12的动物瓣膜表面的微生物密度与接种亲本菌株的动物相当。这些结果表明，金黄色葡萄球菌与血小板的直接结合是心内膜炎发病机制中毒力的主要决定因素。葡萄球菌与血小板的结合似乎对瓣膜表面初始定植后发生的致病事件至关重要，如赘生物形成和脓毒性栓塞。
