Regulation of Salmonella typhimurium pathogenesis

Identification of novel genes involved in Salmonella typhimurium pathogenesis

The project concerns the regulation of virulence genes involved in the pathogenesis of  Salmonella typhimurium, a facultative, intracellular intestinal pathogen (enteropathogen), capable of invasion of host intestinal epithelial cells and survival within phagocytic immune cells such as macrophage and dendritic cells. Carriage of Salmonella by phagocytic cells to lymphoid tissues and organs can lead to long-term infections characterized by shedding into the environment providing a potential reservoir for zoonotic infections of other animals and humans. One prerequisite of the carrier function of phagocytes is the establishment of a protected niche by Salmonella within these cells where it replicates and later infects new cells and cause systemic disease.

Salmonella genomic microarray for determination of global gene expression patterns. The levels of individual gene expression are determinied by measuring the ratio of cDNA fluorescence (green) to the internal hybridization/normalization control genomic DNA fluorescence (red). In this manner, independent experiments can be compared to one another by normalizing to the genomic DNA hybridization which is constant for all arrays.

While a number of Salmonella-specific gene products have been identified which are involved in the interference with host cell processes such as phagocytosis and inhibition of endosome/lysosome fusion, few Salmonella-encoded genes involved growth within the intracellular phagosome have so far been characterized. Previous studies in our group have shown that virulence genes required for both invasion and intracellular replication are regulated by the bacterial signal molecule, guanosine tetraphosphate (ppGpp), which is part of a highly conserved regulatory system in bacteria required for the integration of environmental signals for the regulation of growth and virulence. A mutant defective in production of ppGpp is non-invasive for epithelial cells, shows severe defects in intracellular growth and survival in macrophage, and is completely avirulent in mice. Since all virulence genes remain intact in this mutant strain, only the expression of genes required for virulence are affected.
We are using microarray analysis combined with directed mutagenesis to compare the global gene expression profiles of wildtype and mutant strains to identify and characterize potential regulators and factors in the Salmonella genome involved in invasion and intracellular growth and survival within host cells.

 

Co-workers:

Dr. Karsten Tedin

Grants and Fundingl:

Deutsche Forschungsgemeinschaft (DFG) Graduiertenkolleg Grant 1121/A3

Collaboration with:

- Drs. J.C.D. Hinton and Arthur Thompson, Molecular Microbiology Group, Institute for Food Research, Norwich, England
- Dr. Javier Pizarro-Cerdá, Institut Pasteur, Paris, France
- Dr. Jörg Vogel, Max-Planck Institut für Infektionsbiologie, Berlin, Germany

Selected publications:

Sittka, A., V. Pfeiffer, K. Tedin and J. Vogel (2007) The RNA chaperone Hfq is essential for the virulence of Salmonella typhimurium. Mol. Microbiol. 63:193-217.

Thompson, A., M.D. Rolfe, S. Lucchini, P. Schwerk, J.C.D. Hinton and K. Tedin. (2006) The bacterial signal molecule, ppGpp, mediates the environmental regulation of both the invasion and intracellular virulence gene programs of Salmonella. J. Biol. Chem.281:30112-30121.

Pizarro-Cerdá, J. and K. Tedin. (2004) The bacterial signal molecule, ppGpp, regulates Salmonella virulence gene expression. Mol. Microbiol. 52:1827-1844.

Tedin, K. and F. Norel. (2001) Comparison of DrelA strains of Escherichia coli and Salmonella typhimurium suggests a role for ppGpp in attenuation regulation of branched chain amino acid biosynthesis. J. Bacteriol. 183:6184-6196.

 

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