Molecular analysis of Salmonella typhi host specificity

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Salmonella enterica causes of a large variety of diseases in humans and animals. Understanding pathogenic mechanisms of S. enterica serovar Typhi, the etiologic agent of typhoid fever, is limited by lack of virulence in laboratory animals. Typhi is a host-adapted serovar that is specific for humans. Our long-term objective is to better understand the molecular mechanisms by which Salmonella causes infection and disease in humans. We will focus our research on understanding Typhi host specificity with extensive use of human and murine cell culture models to elucidate differences in bacterial gene expression and survival within cells from these two different host species. Specifically, we will conduct studies to establish a genetic basis for the host specificity of Typhi by : (1) characterizing Typhi specific genes expressed in macrophages that are absent from the serovar Typhimurium genome and (2) identification of Typhi genes that are specifically expressed in only one type of host cells. In these studies, we will employ newly developed molecular genetic tools, such as selective capture of transcribed sequences (SCOTS) a technique currently in use by our research group, that identifies bacterial genes expressed in vivo. We will also use an original approach using GFP (green fluorescent protein) gene fusions and cytofluorometry (FACS). This project will involve the generation of mutant strains using defined deletion mutations with suicide vectors and the use of a broad range of methods of microbial genetics, molecular biology, biochemistry, immunology, cell biology, and microscopy. It is anticipated that the research proposed in this application will contribute to our understanding of the means by which Typhi colonizes, invades and overcomes host defenses and causes enteric fever. This information should lead to strategies, including the development of vaccines to reduce likelihood of Salmonella colonization and infection.