Salmonella overview Flashcards
Characteristics of Salmonella
Salmonella is a gram negative rod. There are 2 types of salmonella, typhoidal and non-typhoidal. Non-typhoidal causes less severe diseases.
Diseases caused by salmonella
Enteric fever and gastroenteritis are caused
Adhesion virulence factors - Salmonella
4 types of fimbriae. Type 1 helps bind to microvilli, plasma (pSLT) encoded helps adhere to microvilli, thin aggregative fimbriae binds bacteria together, long polar fimbriae adheres to payers patches
Invasion/replication virulence factors- salmonella
SPI-1 T3SS injects effector proteins into the cell which activates Rho-GTPase and MPAK pathway, this allows for bacteria to enter the cell and go through tight junctions as well as induce inflammatory response.
SPI2 T3SS comes into effect after epithelial barrier has been crossed. Introduces 30 effector proteins into endomembrane system and cytoplasm which leads to intracellular replication of salmonella and allows for salmonella containing vacuole trafficking.
Virulence factors which aid in competition - salmonella
SopE (part of SPI-1 T3SS) produces nitrate for nitrate respiration. Can use tetrathionate from neutrophils as oxygen radicals. Salmochelin is not effected by sequestering of siderophores, meaning they can still find and bind iron.
Evasion virulence factors - salmonella
RcK produces OMP which prevents formation and insertion of C9 complexes. Spy leads to survival in macrophages and translocation across membrane. Encodes ADP-ribosylating toxin which modifies actin. SPI-2 and SPI-1 proteins can dampen local inflammation.
Which virulence factor is only associated with typhoidal salmonella (not non-typhoidal), what does it do
Vi antigen on capsular polysaccharide. Leads to anti-opsonic and anti-phagocytic properties. Reduces TNFa secretion and increases resistance to oxidative killing
Pathogenesis of Non-typhoidal salmonella
Once non-typhoidal salmonella reaches the small intestine. It is taken up by M cells and is passed on to macrophages which it can survive in and therefore pass through the epithelial cell. It can also enter through epithelial cells through attachment of microvilli and transport into the cell throughSPI-1 T3SS. Dendritic cells can also take up salmonella cells and enter through that.
Pathogenesis for Typhoidal salmonella
There are 3 pathways for Typhoid fever. All pathways first must enter through ingestion and travel to the small intestine.
The first pathway goes from the small intestine and colonises payers patches via Long polar fimbriae
The second pathway will enter the blood stream inducing bacteraemia before it then colonises the first lymph node as well as other organs. It will then colonise the gall bladder and from there will either become a carrier state or reinfect the GI tract and progress along the third pathway
The third pathway will become septicemic and colonise and replicate in the blood stream, inducing typhoid fever
How is salmonella detected
Through PMN amounts in fecal samples. High amount means non-typhoidal, low amounts mean Typhoidal.
How is salmonella treated
Generally just rehydration and electrolyte replacement. For typhoidal, antibiotics are also used
