Bacterial Pathogens and Diseases II (Endotoxins)

Question 1

What layer is a gram negative bacteria cell wall and what is it like compared to gram positive bacteria?

Answer 1

Peptidoglycan layer is very thin compared to gram positive bacteria

Question 2

What does the outer membrane consist of in gram negative bacteria cell wall?

Answer 2

• Has an outer membrane which consists of:
○ Proteins
○ Porins what allow movement of materials
○ Lipopolysaccharide

Question 3

What is Lipid A in lipopolysaccharide?

Answer 3

○ Phosphorylated glucosamines attached to long chain fatty acids

Question 4

Is lipid A hydrophobic?

Answer 4

○ Lipid A is hydrophobic and repels water soluble material

Question 5

What does the polysaccharide core in lipopolysaccharide consist of?

Answer 5

○ Consists of ketodeoxyoctanoic acid(KDO) and heptose

Question 6

Is the polysaccharide core hydrophilic?

Answer 6

○ Hydrophilic and attracts water soluble material

Question 7

What is the O-side chain in lipopolysaccharide?

Answer 7

○ Repeated units of tri/tetra/penta saccharide sugars

Question 8

Is the O side chain hydrophilic?

Answer 8

Hydrophilic

Question 9

What is an endotoxin?

Answer 9

Endotoxin is a lipopolysaccharide

Question 10

What is the active component of endotoxin?

Answer 10

Lipid A is the active component

Question 11

What are endotoxins only found in?

Answer 11

• Found only in gram negative bacteria

Question 12

What are endotoxins major initiators of?

Answer 12

• Major initiator of sepsis pathway

Question 13

What is sepsis?

Answer 13

Sepsis is a life threatening organ dysfunction caused by a dysregulated host response to infection

Question 14

What is sepsis primarily driven by?

Answer 14

• Primarily driven by the innate immune system response:
	○ Macrophages
	○ Monocytes 
	○ Granulocytes
	○ Natural killer cells
        ○ Dendritic cells

Question 15

What do cells of the immune system detect in sepsis?

Answer 15

○ Pathogen associated molecular patters(PAMPs)

○ Damage associated molecular patterns(DAMPs) from damaged host cells

Question 16

What is detection of cells of the immune system mediated by in sepsis?

Answer 16

○ Cell membrane receptors
	§ TLR
	§ C type lectin receptors
○ Cytosol receptors
	§ NOD like receptors
        § RIG-1 like receptors

Question 17

What is the effect after detection by cells of immune system in sepsis?

Answer 17

○ Production of pro-inflammatory cytokines
§ TNFa
§ IL-1
§ IL-6
○ Produce IL-1B and IL-18 through inflammasomes
§ Causes rapid programmed cell death

Question 18

What are the effects of pro-inflammatory cytokines?

Answer 18

1. Increase number, lifespan and activation state of innate immune cells
2. Increase adhesion molecule and chemokine expression by endothelial cells
3. Increase acute phase proteins such as complement, fibrinogen and CRP
4. Cause fever
5. Causes neutrophils to release extra-cellular traps(NETs) made of DNA and antimicrobial proteins that forms a scaffold for platelet activation
6. Cause release of microparticles by activated platelets
7. Increase tissue factor expression by blood monocytes

Question 19

What are 5+6+7 involved in, in the effects of pro inflammatory cytokines?

Answer 19

• 5+6+7 are involved in the formation of thrombus-microbes trapped within this and this attracts and activates further leucocytes

Question 20

What is the dysregulation of sepsis?

Answer 20

• Production of reactive oxygen species which damages cellular proteins, DNA and lipids and impairs mitochondria
• Complement activation causes. An increase In ROS, granulocyte enzyme release, endothelial permeability and tissue factor expression
• Widespread immunothrombosis leading to disseminated intravascular coagulation with impaired microvasculature function and organ dysfunction
• Mitochondrial damage leads to decreased intracellular ATP and cells enter state of hibernation and exacerbates organ dysfunction

Question 21

What type of process is the resolution of sepsis?

Answer 21

• Process of resolution is an active process, not passive

Question 22

What is produced earlier in the process in the resolution of sepsis?

Answer 22

• Anti-inflammatory IL-10 is produced earlier in the process:

Question 23

What does IL-10 suppress production of?

Answer 23

○ Supresses production of IL-6 and gamma interferon

Question 24

What does IL-10 stimulate the production of?

Answer 24

○ Stimulates the production of soluble TNF receptor and IL-1 receptor antagonist

Question 25

What autophagy occurs in the resolution of sepsis?

Answer 25

• Autophagy of PAMPs and DAMPs

§Removal by macrophages

Question 26

What do damaged cells undergo in the resolution of sepsis?

Answer 26

• Damaged cells undergo apoptosis and engulfment by macrophages

Question 27

What is meningococcal sepsis caused by?

Answer 27

• Caused by Neisseria meningitidis

Question 28

What is Neisseria meningitidis?

Answer 28

•A Gram negative diplococcus

Question 29

What can Niesseria meningitidis cause?

Answer 29

• Can cause disease ranging from meningitis to life threatening meningococcal sepsis

Question 30

What makes meningococcus so effective in sepsis?

Answer 30

• Has hexa-acylated lipid A
○ 6 fatty acid chains make it highly effective
• Doesn’t have long-chain fatty acid at the end
• End chain is similar to carbohydrates that are expressed in human cells
○ This is terminal residue mimicry hence immune response isn’t very effective
• Blebs are large chunks of outer cell membrane which are being shed constantly and produce a large amount of LPS