The Research Institute at Nationwide Children's, Center for Microbial Pathogenesis, Columbus, Ohio, United States of America.
PLoS Pathog. 2013;9(10):e1003709. doi: 10.1371/journal.ppat.1003709. Epub 2013 Oct 10.
In an effort to suppress microbial outgrowth, the host sequesters essential nutrients in a process termed nutritional immunity. However, inflammatory responses to bacterial insult can restore nutritional resources. Given that nutrient availability modulates virulence factor production and biofilm formation by other bacterial species, we hypothesized that fluctuations in heme-iron availability, particularly at privileged sites, would similarly influence Haemophilus biofilm formation and pathogenesis. Thus, we cultured Haemophilus through sequential heme-iron deplete and heme-iron replete media to determine the effect of transient depletion of internal stores of heme-iron on multiple pathogenic phenotypes. We observed that prior heme-iron restriction potentiates biofilm changes for at least 72 hours that include increased peak height and architectural complexity as compared to biofilms initiated from heme-iron replete bacteria, suggesting a mechanism for epigenetic responses that participate in the changes observed. Additionally, in a co-infection model for human otitis media, heme-iron restricted Haemophilus, although accounting for only 10% of the inoculum (90% heme-iron replete), represented up to 99% of the organisms recovered at 4 days. These data indicate that fluctuations in heme-iron availability promote a survival advantage during disease. Filamentation mediated by a SulA-related ortholog was required for optimal biofilm peak height and persistence during experimental otitis media. Moreover, severity of disease in response to heme-iron restricted Haemophilus was reduced as evidenced by lack of mucosal destruction, decreased erythema, hemorrhagic foci and vasodilatation. Transient restriction of heme-iron also promoted productive invasion events leading to the development of intracellular bacterial communities. Taken together, these data suggest that nutritional immunity, may, in fact, foster long-term phenotypic changes that better equip bacteria for survival at infectious sites.
为了抑制微生物的生长,宿主通过一种称为营养免疫的过程将必需的营养物质隔离起来。然而,细菌感染引起的炎症反应可以恢复营养资源。鉴于营养物质的可用性会调节其他细菌的毒力因子产生和生物膜形成,我们假设血红素铁可用性的波动,特别是在特权部位,也会类似地影响嗜血杆菌生物膜的形成和发病机制。因此,我们通过连续的血红素铁耗尽和血红素铁补充培养基培养嗜血杆菌,以确定内部血红素铁储存的短暂耗尽对多种致病表型的影响。我们观察到,先前的血红素铁限制增强了生物膜的变化,至少在 72 小时内,与从血红素铁补充细菌起始的生物膜相比,增加了峰值高度和结构复杂性,这表明参与观察到的变化的表观遗传反应的机制。此外,在人类中耳炎的共感染模型中,血红素铁限制的嗜血杆菌尽管仅占接种物的 10%(90%的血红素铁补充),但在 4 天时可回收的生物量高达 99%。这些数据表明,血红素铁可用性的波动促进了疾病期间的生存优势。由 SulA 相关同源物介导的丝化对于实验性中耳炎中最佳生物膜峰值高度和持久性是必需的。此外,血红素铁限制的嗜血杆菌引起的疾病严重程度降低,表现为粘膜破坏减少、红斑减少、出血焦点和血管扩张减少。血红素铁的短暂限制也促进了有生产力的入侵事件,导致细胞内细菌群落的发展。总的来说,这些数据表明,营养免疫实际上可能促进长期的表型变化,使细菌更能在感染部位生存。