Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, and Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02114.
Microbiol Spectr. 2014 Oct;2(5). doi: 10.1128/microbiolspec.PLAS-0002-2013.
Gram-positive bacteria are leading causes of many types of human infection, including pneumonia, skin and nasopharyngeal infections, as well as urinary tract and surgical wound infections among hospitalized patients. These infections have become particularly problematic because many of the species causing them have become highly resistant to antibiotics. The role of mobile genetic elements, such as plasmids, in the dissemination of antibiotic resistance among Gram-positive bacteria has been well studied; less well understood is the role of mobile elements in the evolution and spread of virulence traits among these pathogens. While these organisms are leading agents of infection, they are also prominent members of the human commensal ecology. It appears that these bacteria are able to take advantage of the intimate association between host and commensal, via virulence traits that exacerbate infection and cause disease. However, evolution into an obligate pathogen has not occurred, presumably because it would lead to rejection of pathogenic organisms from the host ecology. Instead, in organisms that exist as both commensal and pathogen, selection has favored the development of mechanisms for variability. As a result, many virulence traits are localized on mobile genetic elements, such as virulence plasmids and pathogenicity islands. Virulence traits may occur within a minority of isolates of a given species, but these minority populations have nonetheless emerged as a leading problem in infectious disease. This chapter reviews virulence plasmids in nonsporulating Gram-positive bacteria, and examines their contribution to disease pathogenesis.
革兰氏阳性菌是许多类型人类感染的主要原因，包括肺炎、皮肤和鼻咽感染，以及住院患者的尿路感染和手术伤口感染。这些感染变得特别成问题，是因为引起它们的许多物种对抗生素具有高度耐药性。移动遗传元件（如质粒）在革兰氏阳性菌中抗生素耐药性传播中的作用已得到充分研究；而移动元件在这些病原体毒力特征的进化和传播中的作用则理解得较少。虽然这些生物体是主要的感染源，但它们也是人类共生生态系统中的重要成员。似乎这些细菌能够利用宿主和共生体之间的密切联系，通过加剧感染和导致疾病的毒力特征来利用这种联系。然而，它们并没有进化为专性病原体，大概是因为这会导致宿主生态系统排斥病原体。相反，在既是共生体又是病原体的生物体中，选择有利于发展可变性的机制。因此，许多毒力特征定位于移动遗传元件上，如毒力质粒和致病性岛。毒力特征可能存在于给定物种的少数分离株中，但这些少数群体仍然成为传染病的主要问题。本章综述了非孢子形成革兰氏阳性菌中的毒力质粒，并探讨了它们对疾病发病机制的贡献。
