8. Shigella Flashcards
What does Shigella induce in macrophages?
Pyroptosis - form of cell death that is triggered by pro-inflammatory signals and associated with inflammation
What disease does the Shigella toxin cause?
Dysentery / Shigellosis
How does the Shigella toxin cause dysentery?
Invasion, A-B toxin, T3SS
What is another name for Shigellosis?
Bacillary dysentery
What are the 4 types of shigella?
S. sonnei
S. flexneri
S. boydii
S. dysentariae
What types of shigella are the most common causes of shigellosis?
S. sonnei
S. flexneri
What is the most severe type of shigella?
S. dysenteriae
List the Shigella (genus) sonnei/ flexneri/ boydii/ dysenteriae characteristics?
Gram negative
Rod-shaped
Non-motile
>90% related to E. coli
What is dysentery characterised by?
Diarrhoea with blood & mucous
Does dysentery usually progress to septicaemia?
No - bacteria don’t usually spread and get into the blood unless a person is immunocompromised
How is Shigella transmitted?
Via water & food
Is Shigella highly infectious?
Yes (ID50 of 100-200)
3rd most common GI pathogen
True or False: Humans are the only known natural host for Shigella
True
Are there antibiotic-resistant strains of Shigella?
Yes
Is there a vaccine for Shigella?
No
Describe the pathogenesis of Shigella
- Attachment: adhesins not identified by may involve the produce of ipaD & ipaB genes
- Invasion: rearrangement of host cell actin filaments → inject proteins into the epithelial cell to induce phagocytosis
- Growth: activated by pH drop, cells escape from vesicle & grow rapidly in cytoplasm (may be mediated by ipaB)
- Spread (a consequence of actin rearrangment)
What are the 4 stages of pathogenesis of shigella?
Attachment - Invasion - Growth - Spread
Pathogenicity of Shigella is associated with what?
The presence of a large virulence plasmid i.e they are mobile
Which cells do Shigella not adhere to?
Polarised cells
What is the Type 3 Secretion System (T3SS)?
A protein needle-like complex that functions as a bacterial delivery system to inject bacterial proteins (effectors) directly from the bacterial cytoplasm into the host cytosol
Effector proteins from T3SS interfere with?
Host signalling pathways
Examples of pathogenic bacteria with a T3SS?
Shigella, Salmonella, EPEC, EHEC, Yersinia
How does Shigella use the T3SS?
Shigella flexneri uses T3SS to gain entrance to host cell. Carries needle-like structures on its surface that make initial contact with host cell & form a pore in its plasma membrane. Shigella then injects proteins that interact with the actin cytoskeleton.
How does Shigella gain entry to the host cell?
M cells