Molecular characterization of Salmonella host specificity

本研究计划的目的是确定相关细菌的宿主趋向性的分子和遗传基础。我们的细菌模型是肠炎沙门氏菌，加拿大领先的食源性细菌病原体之一。沙门氏菌菌株分为血清型，有些只对一个宿主有特异性，而另一些则可以在多个宿主物种中定植。有2600种血清型，目前还没有办法预测它们的宿主范围或毒性。我们建议比较和研究一种仅对人类特异性的血清型，即宿主特异性的伤寒沙门氏菌和一种广泛宿主范围的伤寒沙门氏菌。我们已经观察到这些血清型之间的许多表型差异，我们将通过识别参与宿主适应的基因来进行研究。

The aim of this research program is to define the molecular and genetic basis of host tropism in related bacteria. Our bacterial model is Salmonella enterica, one of the leading foodborne bacterial pathogens in Canada. Salmonella strains are classified into serovars, some are specific to only one host, whereas others can colonize multiple host species. There are 2600 serovars and there is no way yet to predict their host range or virulence. We propose to compare and study a serovar that is specific only to humans, the host-specific S. Typhi and a broad-host range serovar, the generalist S. Typhimurium. We have already observed many phenotypic differences between these serovars and we will pursue by identifying genes involved in host adaptation. Biofilm is an adaptation mechanism in which the bacterium is embedded in an extracellular matrix to protect itself and persist. In Salmonella, the generalist produces biofilm in the environment while the host-specific serovar produces biofilm within the host. The major components of the biofilm matrix, cellulose and the curli adhesin, are not expressed by the host-specific serovar. We have demonstrated that the generalist produces less biofilm in the presence of bile, a substance found in the gut, whereas the host-specific serovar produce more biofilm in the presence of bile. Thus, we hypothesize that biofilm formation is critically linked to host specificity. We will investigate and compare biofilm produced by either the generalist or the host-specific serovar. First, we will characterize Salmonella biofilms in the presence of bile by determining the biomass, the matrix composition, organization and viability. Innovative, qualitative and quantitative approaches will be used to observed biofilm formation in real-time. We will then identify key factors involved in biofilm formation using a high-throughput robotic platform. We will also investigate the influence of microbiota on biofilm formation. Finally, we will investigate the influence of host cell type and origin on Salmonella biofilm formation. Comparison between these two distinctly adapted serovars will lead to the identification of key components that should shed light on specific mechanisms of host adaptation. It is anticipated that the research proposed in this application will contribute to our understanding of basic mechanisms of bacterial biofilm formation and species evolution. As some of the targeted systems are conserved among other bacteria, this may potentially lead to common strategies to potentially reduce the presence of such bacteria in different environments, both within the host and in environmental settings, such as in water and food sources.