Margolis Elisa, Levin Bruce R
Department of Biology, Emory University, Atlanta, GA, 30322, USA.
J Infect Dis. 2007 Oct 1;196(7):1068-75. doi: 10.1086/520934. Epub 2007 Aug 27.
Many bacteria responsible for clinically relevant disease reside harmlessly in a large fraction of humans. Three explanations have been proposed to account for why these normally commensal bacteria occasionally cause invasive disease: host susceptibility, stochasticity in the host-bacteria interaction, and the evolution of invasive mutants in colonized hosts. Here we test the third of these hypotheses for the rare invasiveness of commensal bacteria: within-host evolution.
Using neonatal rats intranasally colonized with pairs of marked Haemophilus influenzae type b strains, we demonstrate that the resulting bacteremias are derived from single organisms. To test the within-host evolution hypothesis we explored the relative ability of bacteria isolated from the blood and nasal passages of bacteremic rats to colonize the nasopharynx and invade the bloodstream.
Our results provide support for within-host evolution as one but not the sole explanation for the invasiveness of these bacteria. We discuss the implications of these results for both the rare invasiveness of commensal bacteria and the general observation that bacteria isolated from the sites of human invasive disease are almost invariably monoclonal.
许多引发临床相关疾病的细菌在很大一部分人体内无害地存在。针对这些通常共生的细菌为何偶尔会引发侵袭性疾病，人们提出了三种解释：宿主易感性、宿主与细菌相互作用中的随机性，以及定殖宿主中侵袭性突变体的进化。在此，我们针对共生细菌罕见的侵袭性检验这些假说中的第三条：宿主体内进化。
使用经鼻内接种成对标记的b型流感嗜血杆菌菌株的新生大鼠，我们证明由此产生的菌血症源自单一生物体。为检验宿主体内进化假说，我们探究了从菌血症大鼠的血液和鼻腔中分离出的细菌定殖鼻咽部并侵入血流的相对能力。
我们的结果支持宿主体内进化是这些细菌侵袭性的一种解释，但并非唯一解释。我们讨论了这些结果对于共生细菌罕见侵袭性以及从人类侵袭性疾病部位分离出的细菌几乎总是单克隆这一普遍观察结果的意义。
