Ravishankar Sumedha, Tuohey Samantha M, Ramos Nicole O, Uchiyama Satoshi, Hayes Megan I, Kang Kalisa, Nizet Victor, Madigan Cressida A
School of Biological Sciences, UC San Diego, La Jolla, California, United States of America.
Biological Sciences Graduate Program, UC San Diego, La Jolla, California, United States of America.
PLoS Biol. 2025 Jul 3;23(7):e3003236. doi: 10.1371/journal.pbio.3003236. eCollection 2025 Jul.
To cause meningitis, bacteria move from the bloodstream to the brain, crossing the endothelial cells of the blood-brain barrier. Most studies on how bacteria cross the blood-brain barrier have been performed in vitro using cultured endothelial cells, due to a paucity of animal models. Group B Streptococcus (GBS) is the leading cause of bacterial meningitis in neonates and is primarily thought to cross the blood-brain barrier by transcytosis through endothelial cells. To test this hypothesis in vivo, we used optically transparent zebrafish larvae. Time-lapse confocal microscopy revealed that GBS forms extracellular microcolonies in brain blood vessels and causes perforation and lysis of blood-brain barrier endothelial cells, which promotes bacterial entry into the brain. Vessels infected with GBS microcolonies were distorted and contained thrombi. Inhibition of clotting worsened brain invasion, suggesting a host-protective role for thrombi. The GBS lysin cylE, implicated in brain invasion in vitro, was found dispensable in vivo. Instead, pro-inflammatory mediators associated with endothelial cell damage and blood-brain barrier breakdown were specifically upregulated in the zebrafish head upon GBS entry into the brain. Therefore, GBS crosses the blood-brain barrier in vivo not by transcytosis, but by endothelial cell lysis and death. Given that we observe the same invasion route for a meningitis-associated strain of Streptococcus pneumoniae, our findings suggest that streptococcal infection of brain blood vessels triggers endothelial cell inflammation and lysis, thereby facilitating brain invasion.
为引发脑膜炎，细菌从血液进入大脑，穿过血脑屏障的内皮细胞。由于动物模型匮乏，大多数关于细菌如何穿过血脑屏障的研究都是在体外使用培养的内皮细胞进行的。B族链球菌（GBS）是新生儿细菌性脑膜炎的主要病因，主要被认为是通过内皮细胞的转胞吞作用穿过血脑屏障。为了在体内验证这一假设，我们使用了光学透明的斑马鱼幼体。延时共聚焦显微镜显示，GBS在脑血管中形成细胞外微菌落，并导致血脑屏障内皮细胞穿孔和裂解，从而促进细菌进入大脑。感染GBS微菌落的血管发生扭曲并含有血栓。抑制凝血会加重脑部感染，表明血栓具有宿主保护作用。在体外与脑部感染有关的GBS溶素cylE，在体内被发现是可有可无的。相反，在GBS进入大脑后，斑马鱼头部与内皮细胞损伤和血脑屏障破坏相关的促炎介质会特异性上调。因此，GBS在体内穿过血脑屏障不是通过转胞吞作用，而是通过内皮细胞裂解和死亡。鉴于我们观察到与脑膜炎相关的肺炎链球菌菌株有相同的侵入途径，我们的研究结果表明，脑血管的链球菌感染会引发内皮细胞炎症和裂解，从而促进脑部感染。
