Application of proteomics to investigate the differential virulence and tropism of Salmonella serovars in food-producing animals

Salmonella enterica is a zoonotic and facultative intracellular pathogen of worldwide importance. Infections present in a variety of ways and range from asymptomatic colonisation to inflammatory diarrhoea or typhoid fever depending on serovar- and host-specific factors. Human diarrhoeal infection is commonly acquired from the food chain and farm environment through the ability of selected non-typhoidal serovars to colonise the intestines of food-producing animals and contaminate the avian reproductive tract and egg. Colonisation of reservoir hosts often occurs in the absence of clinical symptoms, however some S. enterica serovars pose a threat to animal health owing to their ability to cause acute enteritis or translocate from the intestines to other organs causing fever, septicaemia and abortion. Despite the availability of several complete genome sequences of isolates representing several serovars, the molecular mechanisms underlying Salmonella colonisation, pathogenesis and transmission in reservoir hosts remains ill-defined.
This project will utilise proteomics to characterise the repertoire of secreted proteins from Salmonella serovars of different host tropism and that cause different diseases in food-producing animals, namely cattle, chickens and pigs. We propose to study the secreted protein profile of 4 strains for which genomes are available and which have been extensively characterised in food-producing animals. We will focus on the role of secreted proteins, in particular Type Three Secreted effector proteins, due to the wealth of literature supporting a role for these proteins in Salmonella virulence, and indeed virulence of many other pathogenic Gram-negative bacteria. Type 3 secretion systems are complex molecular syringes with proteins spanning both membranes of the bacterium and an external needle through which effector proteins are delivered into the target cell where they subvert cellular processes to the benefit of the pathogen. Comprehensive lists of secreted proteins will be generated for all strains tested and any differentially secreted proteins targeted for further characterisation in models of intracellular bacterial replication after making defined knockout mutations. Defined mutants and complemented strains will be assessed for their ability to survive and/ or replicate in primary macrophages isolated from bone marrow of food-producing animals for example chicken, cow and pig. In addition, the function of any novel secreted proteins will also be characterised using relevant biochemical assays based on sequence homology with known bacterial proteins or the prediction of eukaryotic-like functional domains detected by bioinformatic analysis.
The project will yield valuable information on the molecular basis of tropism and virulence of S. enterica serovars associated with farmed animals. This may, with further development, aid in the development of tools to assess the zoonotic and pathogenic potential of serovars found in farmed animals. Importantly, cross-protective vaccines for control of Salmonella in farmed animals are lacking and the project may identify important conserved antigens for future development.
The student will be registered with the University of Edinburgh and be located at The Roslin Institute. Opportunities will be provided for postgraduate training and travel to relevant national and international conferences. The student will join a vibrant research environment and contribute to high-impact research on the molecular basis of microbial pathogenicity. The project will instil training in diverse areas including computational analysis of genomes, proteomics approaches, molecular methods to manipulate the organism and varied cell culture assays.