Central Facility for Microscopy, Animal Experimental Unit, Helmholtz Centre for Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany.
Biomed Mater. 2017 Sep 13;12(5):055006. doi: 10.1088/1748-605X/aa7667.
Biomaterial-associated Pseudomonas aeruginosa biofilm infections constitute a cascade of host immune reactions ultimately leading to implant failure. Due to the lack of relevant in vivo biofilm models, the majority of the studies report host immune responses to free-living or planktonic bacteria, while bacteria in clinical situations live more frequently as biofilm communities than as single cells. The present study investigated host immune responses to biomaterial-associated P. aeruginosa biofilms in a clinically relevant mouse model. Previously, we reported metallic magnesium, a prospective biodegradable implant, to be permissive for bacterial biofilm in vivo even though it exhibits antibacterial properties in vitro. Therefore, magnesium was employed as biomaterial to investigate in vivo biofilm formation and associated host immune responses by using two P. aeruginosa strains and two mouse strains. P. aeruginosa formed biofilm on subcutaneously implanted magnesium disks. Non-invasive in vivo imaging indicated transient inflammatory responses at control sites, whereas robust prolonged interferon-β (IFN-β) expression was observed from biofilm in a transgenic animal reporter. Furthermore, immunohistology and electron microscopic results showed that bacterial biofilms were located in 2D immediately on the implant surface and at a short distance in the adjacent tissue. These biofilms were surrounded by inflammatory cells (mainly polymorphonuclear cells) compared to the controls. Interestingly, even though the number of live bacteria in various organs remained below detectable levels, splenomegaly indicated systemic inflammatory processes. Overall, these findings confirmed the resistance of biofilm infections in vivo to potentially antibacterial properties of magnesium degradation products. In vivo imaging and histology indicated the induction of both local and systemic host inflammatory responses to P. aeruginosa biofilms. Even though the innate host immune defenses could not eliminate the local infection for up to two weeks, there was no apparent systemic bacteremia and all the animals investigated survived the infection.
生物材料相关铜绿假单胞菌生物膜感染构成了宿主免疫反应级联，最终导致植入物失效。由于缺乏相关的体内生物膜模型，大多数研究报告的是宿主对自由生活或浮游细菌的免疫反应，而在临床情况下，细菌更多地以生物膜群落的形式存在，而不是以单细胞的形式存在。本研究在一种临床相关的小鼠模型中研究了宿主对生物材料相关铜绿假单胞菌生物膜的免疫反应。之前，我们报道了金属镁，一种有前途的可生物降解植入物，即使在体外具有抗菌特性，但在体内仍允许细菌生物膜的形成。因此，采用两种铜绿假单胞菌菌株和两种小鼠品系，利用镁作为生物材料来研究体内生物膜形成及其相关的宿主免疫反应。铜绿假单胞菌在皮下植入的镁盘上形成生物膜。非侵入性的体内成像表明，在对照部位存在短暂的炎症反应，而在转基因动物报告中，从生物膜中观察到了强烈的、持久的干扰素-β（IFN-β）表达。此外，免疫组织化学和电子显微镜结果表明，细菌生物膜位于植入物表面的 2D 处，并在相邻组织中存在较短的距离。与对照相比，这些生物膜被炎症细胞（主要是多形核细胞）包围。有趣的是，尽管在各种器官中的活菌数量仍低于可检测水平，但脾肿大表明存在全身炎症过程。总的来说，这些发现证实了体内生物膜感染对镁降解产物潜在抗菌特性的抵抗力。体内成像和组织学表明，铜绿假单胞菌生物膜诱导了局部和全身宿主炎症反应。尽管先天宿主免疫防御系统不能在两周内消除局部感染，但没有明显的全身菌血症，所有接受检查的动物都存活下来。
