1. Nature reviews Microbiology January 2008

2. Gram-negative Enterobacteria Diameter 0.7 - 1.5 µm S. enterica serovar Typhimurium serovar Typhi Daniel Elmer SalmonTheobald Smith WHO: typhoid fever 16 million cases of per year 600 000 fatal cases Ways of acquirement: - Contaminated food and water - Exposure to reptiles and amphibians Salmonella sp. Diseases range from mild diarrhoea to severe typhoid fever

3. Salmonellae preferably enter microfold (M) cells in the small intestine Severe acute necrotizing enteritis Normal Peyer’s patches and ileum Non typhoid strain infection is limited to intestine Some Salmonella serotypes can cause systemic illness

4. Virulence-associated type III secretion system (T3SS) - mediates the transfer of bacterial proteins into the host cell - found only in Gram-negative, mostly in pathogenic bacteria - evolutionary related to flagellar system FlagellumT3SS

5. 9 KDa T3S proteins 100-150 subunits Length: 60-80 nm Width: 8 nm Inner diameter: 3 nm Needle complex (NC) Proteins – effectors: N-terminal secretion signal Binding site for chaperone Chaperones can act as transcription factors

6. Two distinct T3SSs are encoded within Salmonella pathogenecity islands (SPI)

7. Salmonella SPI1 encoded type III secretion system and it’s effectors

8. SPI 1 T3SS Activation of the Rho GTPases Actin cytoskeleton rearrangement Bacterial-mediated endocytosis

9. Salmonella SPI1 encoded type III secretion system and it’s effectors

10. Tight junctions destabilization Transepithelial migration Intestinal inflammatory responses Normal structure regainment SPI 1 T3SS Salmonellae might be evolving towards parasitism or commensalism

11. Effectors of the Salmonella SPI2 encoded type III secretion system

12. Salmonella containing vesicles (SCV) and SPI 2 T3SS SCV – unique phagosome, can persist intracellularly up to several days Associated with early, late endosomal as well as lysosomal markers Moves to perinuclear position, associated with Golgi SCV is believed to be a niche for Salmonellae replication

13. Effectors of the Salmonella SPI2 encoded type III secretion system

14. Formation of the Salmonella induced filaments (Sifs) The importance of the Sif formation is currently not understood - promotes bacterial replication via increasing the size of the SCV - redirects nutrient-rich organellas to the SCV Sifs - originate from the SCV and extend throughout the cell Possible mechanism - vesicle budding from SCV Requires microtubules, kinesin, dynein, Salmonella SifA and PipB2 effectors

15. Sensing and response to the vacuole LPS Antimicrobial peptides: PhoQ sensor and surface remodelling Decreasing length of the O antigen Alterations in lipid A Oxygen and nitrogen radicals: Cu,Zn superoxid dismutases 919 genes in S. typhimurium are upregulated in phagosome

16. Summary Salmonellae encode two virulence-associated T3SS: SPI 1 T3SS translocates effectors across the plasma membrane - rearrangement of the actin cytoskeleton - destabilization of the tight junctions - entry into non-phagocytic cells by bacterial-mediated endocytosis - partial blocking of the NF-kB activity SPI 2 T3SS translocates effectors across the vacuolar membrane - Sif formation - SCV movement to perinuclear position - rearrangement of the cell organells - transport of metabolic molecules into the SCV - promotes bacterial replication within host cell Salmonellae can sense phagosomal environment and are able to induce various systems to promote intracellular survival

17. Thank you for your attention!