Lecture A8/A9 - Salmonella Flashcards
What type of bacteria are salmonella?
Gram negative.
What salmonella causes food poisoning?
Salmonella typhimurimum + enterica
What salmonella causes typhoid fever?
S. typhi
What are pathogenicity islands?
Chunks of DNA that have been acquired horizontally from other bacteria.
What are the main salmonella pathogenicity islands?
SPI1 SPI2
What does SPI1 and SPI2 code for?
Special type 3 secretion system (T3SS) enabling the bacteria to inject into proteins on the host cells.
How does the T3SS work?
Allows salmonella to invade cells that doesn’t want to take it up.
Secretes proteins from the bacterial cytoplasm through the basal body and the needle into the intestinal cells.
They can then interfere with the cytoskeleton causing actin polymerisation (ruffling) causing engulfment of salmonella.
Describe SPI1 T3SS signals and mechanisms.
Injects effector proteins causing cytoskeletal rearrangements to force the intestinal epithelial cells to take it up.
Basal body and needle.
Postcodes on proteins tell them where to go as well as sequences for chaperones to help direct the proteins to the basal body and denature the protein to thread it through the needle.
What intestinal mucosal epithelia cells take up salmonella?
M cells
Dendritic cells
Describe how M cells structure provides an entry target for pathogens.
The apical surface of M cells is not covered by the mucus layer and transfer the endosomal contents to the basolateral surface to the underlying MALT.
When does SPI2 operate?
When the salmonella is inside cells.
Operates in the vacuole salmonella is in.
How does capase 1 cause inflammation in salmonella infection?
Long needle in T3SS is made up of PrgJ.
Translocation of flagellin and PrgJ detected by NLR4 to form a complex with capase 1 resulting in cleavage and activation of capsase 1 = inflammation.
Describe ileal secretion.
Severe salmonella caused by high levels of fluid secretion into intestines.
Effector molecules cause secretion of fluid into the intestine.
Inflammation and migration of neutrophils damages the intestinal barrier allowing the movement of chloride ions into the intestine.
This disseminates salmonella into the environment, spreading it.
How does salmonella escape into the lumen and infect additional cells or exit the host to transmit?
Extrusion - cells destined to die signal to surrounding epithelial cells to contract an actomyosin ring to squeeze them out. During salmonella extrusion rates increase and 10% of infected cells undergo extrusion followed by inflammatory cell death.
What are the salmonella strategies for escaping colonisation resistance?
Hydrogen boost
Intestinal inflammation provides respiratory electron acceptors for salmonella.
Host derived nitrate boosts growth in inflamed gut.
Ethanolamine competes with microbiota.
Chemotaxis and flagella.
