Lecture 13

Question 1

What are the antimicrobial properties of phagocytosis?

Answer 1

1. low pH (V-ATPase)
2. Production of reactive oxygen species (ROS)
3. Catinonic antimicrobial peptides (CAMPs)
4. Acquisition of proteases (e.g. cathepsins)

Question 2

What is the pH of an immature phagosome compared with a mature phagosome? Why is there a change?

Answer 2

Immature= 7.4

mature= 4.5

Dur to the increase in V-ATPases

Question 3

What are reactive oxygen species and how do they cause damage to cells?

Answer 3

Oxygen derivatives which are highly reactive due to the unpaired electrons they have. Examples are superoxide anions and hydroxyl anions.

Cause damage to macromolecules (DNA, RNA, protein, lipids) by oxidation

Question 4

How do CAMPs kill bacterial cells?

Answer 4

They destabilise biological membranes

Question 5

Whats the structure of CAMPs?

Answer 5

CAMPS have a polar and non-polar surface. The polar surface interacts with the hydrophilic head of the membrane lipid and the non-polar with the hydrophobic tail to get through the inner and outer membrane.

Question 6

How does Superoxide dismutase and catalase protect Salmonella from lysosomes?

Answer 6

These enzymes detoxify the reactive oxygen species within the lysosomes. SOD converts SO to H2O2

Catalase converts H2O2 to water and oxygen

Question 7

What are the two types of secretory systems that are required for survival of Salmonella in the lysosome?

Answer 7

TTSS1 and TTSS2

Question 8

Where does Salmonella reside when in host cells?

Answer 8

In a ‘remodelled’, less acidic lysosomal compartment

Question 9

Describe how the PhoP/PhoQ and PmrA/PmrB regulatory system protects Salmonella when inside the lysosome

Answer 9

PhoQ is phosphorylated at low pH. PhoQ then phosphorylates PhoP. PhoP then activates gene expression to change the lipopolysaccharides. This prevents binding of CAMP.

PmrA/pmrB system is activated by PhopP. PmrB phosphorylated at low pH. PmrB phosphorylates PmrA. PmrA then also changes gene expression to change the LPS to prevent CAMP binding.

CAMPs (+ve parts) bind to LPS (-ve). PhoQ/PhoP and PmrA/PmrB system stimulates gene expression of bacterial genes that covalently modify LPS such than no-longer binds CAMPS.

Question 10

What disease does Leigonella pneumophilia cause?

Answer 10

Leigonnaire’s disease (bacterial pneumonia)

Question 11

Where does Leigonella grow in host cells?

Answer 11

Leigonella-containing vesicles (LCV)

Question 12

In what human cells do Legionella pneumophilia grow?

Answer 12

Macrophages lol

Question 13

What cell function does Legionella hijack to help protect itself in the cell?

Answer 13

Intracellular trafficking from the endoplasmic reticulum. Uses membrane from the ER to surround itself.

Question 14

Why do Legionella live in Legionella containing vacuoles in the host cell? (3)

Answer 14

1. allow efficient growth
2. prevent phagocytic killing
3. creates a niche place for replication

Question 15

What are three reasons Legionella need the Dot/Icm type IV secretion system?

Answer 15

Required for:

1. Acquisition of ER-derived membrane by LCVs
2. Prevention of maturation of LCVs into lysosomes
3. Intracellular growth of Legionella

Question 16

What are the major structural components of Dot/Icm type IV secretion system?

Answer 16

Substrate associated chaperones

ATPases

Inner and outer membrane proteins

Proteins that make a pore in the phagosome membrane

Question 17

What is the Dot/Icm type IV secretory system?

Answer 17

Similar structure to a conjugation system. Used for the transport of around 300 substrate proteins across the bacterial inner and outer membranes and through the host vacuole

Question 18

Listeria monocytogenes- Lysis of the phagosome and escape to the cytosol is mediated by what toxin?

Answer 18

Lysteriolysin O

Question 19

How does lysteriolysin O form pores in membranes?

Answer 19

LLO is a cholesterol dependent pore forming toxin. It binds to membranes and undergoes cholesterol dependent oligomerisation, leading to pore formation in the lipid bilayer.

Question 20

What is Lysteriolysin O activated by? Why?

Answer 20

Activated by low pH. This regulation ensures that LLO exerts its pore forming activity primarily in the phagosome.

Question 21

Listeria monocytogenes push through from one cell to another. What toxin is needed to lyse the double-membraned vacuole that surrounds it after moving?

Answer 21

Lysteriolysin O

Question 22

What is PlcA and what does it do?

Answer 22

A phosphatylinositol specific lipase C, which hydrolyses phospholinositol (PI) in the outer membrane of the phagosome

Question 23

What is PlcB and what does it do?

Answer 23

A broad spectrum phospholipase C that hydrolyses most phospholipids, including phosphatidylcholine (PC) present in both leaflets of the phaogosome

Question 24

What 3 toxins work together to destroy the phagosome encasing Listeria monocytogenes when in the host cell?

Answer 24

LLO, PlcA, and PlcB.

Question 25

What does Listeria use as a food source when its in the cytosol? What enzyme transports this into the cell?

Answer 25

Glucose-1-phosphate. Transported into the cell by hexose phosphate transporter (Hpt)

Question 26

How do Listeria monocytogenes bacteria move through and between host cells?

Answer 26

Actin polymerisation. Addition of actin monomers at the plasma interface generates a protrusive force that drives cell motility