Genetic determinants of systemic host-adapted Salmonella

 描述(申请人提供)：肠道沙门氏菌感染在世界各地的人和牲畜中导致大量的发病率和死亡率。虽然大多数肠出血性沙门氏菌如鼠伤寒沙门氏菌、肠炎沙门氏菌和新港沙门氏菌仍然局限于肠道，并主要在摄入后引起胃肠炎，但那些对宿主适应良好的沙门氏菌，包括人类的伤寒杆菌(伤寒病原体)、猪的霍乱杆菌、都柏林的牛和家禽的加里纳氏杆菌，已经进化成系统性传播，促进败血症，如果不治疗可能导致死亡。这些系统性沙门氏菌经历了广泛的功能丧失突变，主要是在厌氧肠道环境之外不再需要的基因上。尽管已鉴定出一些新获得的促进系统沙门氏菌毒力的基因和宿主适应的等位基因变异，但尚未对系统血清型特有的基因和/或等位基因进行全面的分析。在初步研究中，我们只鉴定了系统性沙门氏菌共有的三个基因，但已经鉴定出所有或大多数败血症血清型共有的许多独特的等位变异。基于这一发现以及新描述的系统性侵袭性非伤寒沙门氏菌与系统性沙门氏菌而不是肠道沙门氏菌具有许多毒力蛋白等位基因的令人兴奋的观察，我们将检验等位基因变异是系统性致病类型的主要决定因素的假设。一项创新和无偏见的全基因组关联研究将专门比较四个系统/宿主适应的血清型和上述三个典型肠道血清型的基因组，以确定促进系统传播和宿主适应的等位基因变体的独特非同义单核苷酸多态。可能参与促进系统性沙门氏菌传播的代谢途径将通过基因浓缩分析来确定。在系统/宿主适应的沙门氏菌中检测到的最具统计学意义的独特等位基因的生物学相关性将在功能分析中进一步研究。将特别注意毒力因素，如 粘附素和3型效应蛋白，重点是那些参与细菌入侵和宿主炎症的蛋白。将对参与代谢途径的蛋白质进行额外的审查，这些代谢途径将在全身环境中提供选择性优势，因为全身环境的含氧量更高，并提供不同的营养和代谢物补充。细菌的结合、侵袭、存活/复制和宿主细胞致死性将通过相应的宿主特异性细胞和敲除突变体、等位基因替换和/或重组体进行评估。通过为人类系统性沙门氏菌病提供更相关的动物模型，确定哪些动物特有的沙门氏菌共有(S)“人类适应的”等位基因将为未来的活体研究提供信息。识别决定人类败血症致病类型的特定等位基因集将突出抗击或预防系统性形式沙门氏菌感染的新靶点。

 DESCRIPTION (provided by applicant): Salmonella enterica infections result in substantial morbidity and mortality in humans and livestock worldwide. While most S. enterica serovars such as Typhimurium, Enteritidis and Newport remain restricted to the intestine and primarily cause gastroenteritis after ingestion, those that are well adapted to a host, including Typhi in humans (the agent of typhoid fever), Choleraesuis in pigs, Dublin in cattle and Gallinarum in poultry, have evolved to spread systemically, promoting sepsis that can lead to death if left untreated. These systemic Salmonella have undergone extensive loss-of-function mutations, mainly in genes that are no longer needed outside of the anaerobic intestinal environment. Although a few newly acquired genes and host-adapted allelic variants promoting virulence in systemic Salmonella have been identified, a comprehensive analysis of genes and/or alleles unique to systemic serovars has not yet been undertaken. In preliminary studies, we have identified only three genes shared by systemic Salmonella, but have identified many unique allelic variants shared among all or most of these septicemic serovars. Based on this finding and the additional exciting observation that newly described systemically invasive non-typhoidal Salmonella share many virulence protein alleles with systemic Salmonella and not with intestinal Salmonella, we will test the hypothesis that allelic variants are major determinants of the systemic pathotype. An innovative and unbiased genome wide association study will specifically compare the genomes of the four systemic/host-adapted serovars with those of the three typical intestinal serovars, all mentioned above, to identify unique nonsynonymous single nucleotide polymorphisms for allelic variants that promote systemic spread and host adaptation. Metabolic pathways potentially involved in promoting systemic Salmonella dissemination will be determined by gene enrichment analysis. The biological relevance of the most statistically significant unique alleles detected in systemic/host-adapted Salmonella will be further investigated in functional assays. Particular attention will be given to virulence factors, such as adhesins and type 3 effector proteins, with a focus on those participating in bacterial invasion and host inflammation. Additional scrutiny will be given to proteins involved in metabolic pathways that would provide a selective advantage in the systemic environment, which is better oxygenated and provides a different complement of nutrients and metabolites. Bacterial binding, invasion, survival/ replication and host cell lethality will be evaluated with corresponding host-specific cells and knock out- mutants, allelic substitutions and/or recombinants. Determining which animal specific Salmonella share(s) "human-adapted" alleles will inform future in vivo studies by providing more relevant animal models for systemic salmonellosis in humans. Identification of specific sets of alleles that dictate a septicemic pathotype in humans will highlight new targets for combatting or preventing the systemic forms of Salmonella infections.