L18: Signal Transduction and Virulence Flashcards
What causes gastroenteritis and enteric fever?
Non-typhoid Salmonella
What causes typhoid fever?
S. typhi
What are the two acidic environments salmonella must survive?
- Stomach
2. Acidic phagocytic vesicle of the macrophage
After surviving the trip through the GI system, salmonella colonize the ___ and invade the ___. This occurs by bacterial-mediated endocytosis. What are the two steps of this process?
Small intestine; M cells; Attachment and entry
In contrast to V. cholerae, Salmonella is a ___ pathogen.
Intracellular
Describe the process of invasion by Salmonella.
Salmonella attaches to the vili of the M cell. The bacterium communicates to the M cell and causes growth of the vili; these engulf the bacteria (ruffling) into a phagosome in the M cell. It passes to the basal side and fuses with macrophages.
After macrophages engulf Salmonella, what happens?
Macrophages carry the bacteria to the reticuloendothelial system and from there into the bloodstream, causing a systemic infection.
What are Type III secretory apparati used for in infection by Salmonella?
- Facilitation of entry into M cells
- Survival in phagosomes
- Survival in macrophages
How does Salmonella facilitate entry into M cells using a Type III secretory apparatus?
SPI1 is a large pathogenicity island that includes inv, spa, and sip. inv and spa encode a Type III secretory system, which exports Sip proteins through the bacterial cell surface into the host M cell. Sip proteins facilitate phagocytosis via ruffling.
Why don’t lysosomes kill bacteria in phagosomes?
Type III secretory apparatus secretes proteins into the M cell cytosol and inhibits phagosome-lysosome fusion
How does the pathogen facilitate entry into macrophages?
Another Type III secretory apparatus (prgHIKL) exports proteins (EPs) through the bacterial cell surface into the macrophage. This facilitates phagocytosis by the macrophage.
Once inside the macrophage, how does S. typhimurium survive?
It represses genes necessary for entry and activates genes necessary to defeat macrophage defenses.
What are the two components of a 2CST (two-component signal transduction)?
- Sensor (histidine autokinase)
2. Response regulator (aspartate autokinase)
What happens when an environmental signal binds to a sensor kinase?
The sensor kinase is autophosphorylated (uses ATP). The response regulator is autophosphorylated (uses sensor kinase). The response regulator is typically a TF that either activates or represses transcription.
Each response regulator is attached to a ___.
Output domain (eg, DNA-binding domain)
