Transmission and biofilm formation by pathogenic Salmonella strains

沙门氏菌是一组致病细菌，可引起哺乳动物（包括人类）、鸟类和爬行动物的感染。尽管对这些病原体进行了100多年的研究，但科学家们仍然不明白沙门氏菌传播的动力学是如何发生的，生存和持续的机制仍然难以捉摸。我的研究方向是沙门氏菌生物膜的形成、毒力、传播和疫苗开发。生物膜是可在生物和非生物表面形成的多细胞聚集细菌群落；这些结构对消毒剂、抗生素以及环境和代谢压力具有高度的抵抗力。在这个建议中，我们将研究沙门氏菌血清鼠伤寒沙门氏菌的生物膜形成，这是世界上最常见的菌株之一。在之前NSERC的一项发现中，我们发现当鼠伤寒沙门氏菌形成生物膜时，细胞群分化为耐药的生物膜细胞和毒力强的单细胞。我们假设这种被称为“表型转换”的策略为鼠伤寒沙门氏菌菌株在进入环境时提供了传播优势。种群的两种细胞类型在不同的环境中各自具有特定的优势，但结合起来将确保通过环境有效地进行传播。我们将研究生物膜在鼠伤寒沙门氏菌通过污染水传播和小鼠感染模型中的作用，并使用转座子测序（Tn-seq）技术鉴定参与长期水生存的基因和在传播过程中至关重要的基因。我们将开发新的遗传工具来测试表型转换是如何调节的，使用现有的荧光标记鼠伤寒沙门氏菌报告菌株（生物膜- gfp；毒性单细胞- mcherry），并试图建立一个双报告菌株，以便我们可以更详细地检查两种细胞类型之间的遗传调控。实验将涉及广泛的体外测试，包括高分辨率、单细胞显微镜和微流体。最后，我们将通过进行细胞因子分析来研究宿主对鼠伤寒沙门氏菌特化细胞类型的反应。这将旨在确定相似性和差异性，以及这与沙门氏菌细胞表面的蛋白质和多糖的关系。生物膜被认为是细菌生命的主要形式，不同基因在传播中的作用是沙门氏菌研究中一个未被探索的领域。我想了解控制表型转换的机制，因为如果我们能理解控制并识别调节这一过程的信号，那么我们就能设计出防止它的策略。最后，与生物膜形成的相似性和传播对病原体进化成功的重要性意味着我们的结果将在整个细菌王国具有广泛的相关性和影响。

Salmonella are a group of pathogenic bacteria that cause infections in mammals (including humans), birds and reptiles. Despite studying these pathogens for over 100 years, scientists still do not understand how the dynamics of Salmonella transmission occur and the mechanisms of survival and persistence remain elusive. My research program is focused on Salmonella biofilm formation, virulence, transmission and vaccine development. Biofilms are multicellular aggregative bacterial communities that may form on living and non-living surfaces; these structures are highly resistant to disinfectants, antibiotics, and environmental and metabolic stress. In this proposal, we will examine biofilm formation in Salmonella serovar Typhimurium, which is one of the most common groups of strains circulating in the world. In a previous NSERC discovery grant we discovered that when S. Typhimurium forms biofilms, the population of cells differentiate into resistant, biofilm cells and virulent, single cells. We hypothesize that this strategy, called `phenotype switching' provides a transmission advantage for S. Typhimurium strains when they pass into the environment. The two cell types of the population each provide specific advantages in different contexts, but together would ensure that transmission through the environment occurs efficiently. We will investigate the role of biofilms in S. Typhimurium transmission via contaminated water and the mouse model of infection, and use a technique called transposon sequencing (Tn-seq) to identify genes involved in long-term water survival and genes that are vital at key points in the transmission process. We will develop new genetic tools to test how phenotype switching is regulated, using existing fluorescently-tagged S. Typhimurium reporter strains (biofilm-GFP; virulent single cells-mCherry) and trying to build a dual-reporter strain so we can examine genetic regulation between the two cell types in a more detailed way. The experiments will involve extensive in vitro testing, including high-resolution, single-cell microscopy and microfluidics. Finally, we will investigate the host response to the specialized cell types of S. Typhimurium by performing cytokine profiling. This will aim to determine similarities and differences and how that relates to proteins and polysaccharides on the Salmonella cell surface. Biofilms are thought to be the predominant form of bacterial life and the role of different genes in transmission is an under explored area in Salmonella research. I want to understand the mechanisms that control phenotype switching, for if we can understand control and identify the signals that regulate this process, then we can design strategies to prevent it. Finally, the similarities with biofilm formation and the importance of transmission for the evolutionary success of pathogens means that our results will have a wide relevance and impact across the bacterial kingdom.