Cellular Microbiology

Question 1

How do bacteria manipulate actin for cell entry? What triggers it?

Answer 1

Trigger: T3SS effectors (eg, salmonella SopE mimics GEFs to activate Rho GTPases leading to actin ruffles).
-Zipper: Adhesions (eg Listeria InIA binds to E-cadherin) and recruits host machinery for uptake.

Question 2

What is actin-based motility? (Give 2 examples.):

Answer 2

• Bacteria polymeriase actin tails to propel through cells.
• Examples (Listeria (ActA) & Shigella (IcsA)

Question 3

How does EPEC form actin pedestals?

Answer 3

T3SS effector Tir binds to host Nck and then recruits N-WASP/Arp2/3, leading to actin polymerisation.

Question 4

Name two Bacterial effectors that inhibit NF-kb and their targets:

Answer 4

-Yersinia YopJ (blocks IKK)
- Shigella OspG (stabilises Ikb)

Question 5

How does Salmonella SopB disrupt TRL4 signalling?

Answer 5

It inhibits the activation of NP-kb activation

Question 6

Which effector blocks STING trafficking?

Answer 6

Shigella IpaJ (protein cleaves host proteins).

Question 7

Compare Listeria and Shigella actin-based motility:

Answer 7

-Listeria: ActA mimics WASP, which directly activates Arp2/3.
- Shigella: IcsA recruits host N-WASP, which activates Arp2/3.

Question 8

How does Yersinia inhibit phagocytosis?

Answer 8

YopE (GAP inactivates Rho GTPases) + YopH (phosphatase disrupts focal adhesions).

Question 9

What is the role of Shigella VirA in entry?

Answer 9

Protease disrupts microtubles, which activates Rac1 and promotes actin polymerisation.

Question 10

Name two PRRs detecting bacterial LPS and DNA:

Answer 10

• T4SS detects Bacterial LPS
  -cGAS detects Bacterial DNA.

Question 11

How do Bacteria inhibit MAPK signalling?

Answer 11

Salmonella ArvA dephosphorylates MAPK and Shigella OspF irreversibly inactivates it.

Question 12

What adaptor does MAVS recruit for RLR signalling?

Answer 12

MAVS activates TBK1 = IRF3/7, which leads to interferon production.