Bacterial Pathogens and Disease II-Endotoxins Flashcards
- What are endotoxins a component of?
•Endotoxins are a component (lipopolysaccharide) of the bacterial polysaccharide wall.
- What is the difference between gram + and gram - plasma membranes?
Both gram – and gram + bacteria have a plasma membrane. Gram + only have a outer peptidylglycan layer whilst gram – also have a second membrane (which contains lipopolysaccharides - endotoxins)
- What three sections of lipopolysaccharides are there?
- Lipid A component
- Core polysaccharide component
- O side chain component
- What is the lipid A component structure?
- hydrophobic or hydrophilic?
- Constant or species dependant?
2 phosphorylated glucosamines attached to long chains of fatty acids that sticks into the outer membrane for anchorage.
o Hydrophobic and the number/type of fatty acids are species dependent.
- What is the core polysaccharide component structure?
- hydrophobic or hydrophilic?
- Constant or species dependant?
unusual sugars (Ketodeoxyoctanoic acid (KDO) and heptose). o Hydrophilic and relatively constant between species of bacteria.
- What is the O side chain component structure ?
- hydrophobic or hydrophilic?
- Constant or species dependant?
: Repeat units of tri, tetra or pentasaccharide sugars
o Hydrophilic, highly variable between species and very antigenically potent chain.
- What component of the lipopolysaccharide drives septic shock?
The lipid A component
- Do immunogenic components drive septic shock?
no
The lipid A component does
- Which component of the lipopolysaccharide is highly immunogenic and immune specific?
- > What does this mean?
The O antigen is highly immunogenic ( easily provoke an immune response) and immune specific (only 1 antibody will be able to recognise this antibody)
- List three characteristics of lipopolysaccharides?
- Only present in gram negative bacteria
- Heat stable
- Not converted to toxoids
- Which pathway do endotoxins initiate?
Sepsis
- What is sepsis?
Life threatening organ dysfunction caused by a dysregulated host immune response to infection.
- Explain how sepsis is driven by the innate immune system- briefly?
- PAMP’s (eg endotoxins) + DAMP’s (from damaged host cells) detected via receptors
- Innate immune response driven
- Gene expression changed
- What does PAMP’s and DAMP’s stand for?
PAMPs = Pathogen associated molecular patterns
DAMPs = Damage associated molecular patterns
- What two types of receptors detect PAMPs and DAMPs and give examples of each?
- Cell membrane receptors - eg Toll like receptors (TLR) or C-type Lectin receptors
- Cytosol receptors - NOD like receptors and RIG-I like receptors
- Like some examples of cells that are apart of the innate immune system?
- Macrophages
- Monocytes
- Granulocytes
- Natural Killer Cells
- Dendritic Cells
- What are the 2 main effects of changing gene expression - (sepsis )??
- Production of pro-inflammatory cytokines (TNF-alpha, IL-1 and IL-6)—-> Recruits an immune response
- Inflammasomes to produce IL-1beta and IL-18 —> Rapid programmed cell death
- What is the mechanism by which endotoxins (specifically Lipid A component) result in an increased pro-inflammatory cytokines and TNF-alpha?
- Lipid A component is recognised by MD-2 so it binds to the lipopolysaccharide.
- This complex then binds to the toll-like receptor which has a coreceptor called CD14.
- This causes dimerisation of the receptor which results in intracellular signalling cascade.
- This activates NF-kB which results in the production of TNF-a and other pro-inflammatory cytokines.
- What are 7 effects of pro-inflammatory cytokines?
Out of these 7 effects, which three form a thrombus (immunothrombus)
- Increase number, lifespan and activation state of innate immune cells.
- Increase adhesion molecule and chemokine expression by endothelial cells.
- Increase acute phase proteins such as complement, fibrinogen and CRP (C-reactive proteins).
- Pro-inflammatory cytokines cause fever.
- Causes neutrophils to release extra-cellular traps (NETs) made of DNA and antimicrobial proteins that forms a scaffold for platelet activation.
- Cause release of microparticles by activated platelets
- Increase tissue factor expression by blood monocytes
5,6,7 = thrombus
- What is a thrombus, what is the result of a thrombus?
A thrombus is a blood clot that forms in a vessel and remains there, microbes are trapped within the thrombus —–> attracts and activates further leucocytes
- What are the 4 ways that lipopolysaccharides act as immunostimulants?
(rapid control of localised and minor infections achieved)
- LPS stimulates macrophages to produce TNF which causes fever and reduces iron (to limit bacterial growth).
- LPS activates receptors on endothelial cells to increase permeability (hypotension leads to septic shock).
- LPS causes mast cells to degranulate and release inflammatory mediators.
- LPS activates platelets, clotting and complement.
- How might LPS cause organ failure
• Organ failure due to increased permeability, hypotension and hypovolaemic shock, fever, disseminated intravascular coagulation and multiple organ failure.
- What happens if the process of LPS acting as immunostimulants passes a certain threshold?
Systemic Injury
- How might immune dysregulation result in sepsis?
4 ways
- Production of ROS eg hydroxyl or NO
- Complement Action (especially C5a)
- Widespread immunothrombin
- Impaired mitochondria
- How might the production of ROS (eg Hydroxyl or NO) result in sepsis?
- > Damages cellular proteins
- > Damages DNA and Lipids
- > Impairs Mitochondria
- How might the complement action( esp C5a) result in sepsis?
increase ROS
granulocyte enzyme release
endothelial permeability
tissue factor expression.
- How might widespread immunothrombosis result in sepsis?
Widespread immunothrombosis leading to disseminated intravascular coagulation (DIC) with impaired microvasculature function and organ dysfunction
- How might mitochondrial damage result in sepsis?
Mitochondrial damage leads to decreased intracellular ATP and cells enter state of hibernation – exacerbates organ dysfunction.
- What are some resolutions of sepsis?
•Active negatively regulated process – not passive.
•Anti-inflammatory IL-10 produced early in process:
o Supresses production IL-6 and γ-interferon
o Stimulates production of soluble TNF receptor and IL-1 receptor antagonist
- Autophagy of PAMP’s and DAMP’s – removal
- Damaged cells undergo apoptosis and engulfment by macrophages.
- A type of sepsis is called Meningococcal sepsis, what is this sepsis caused by?
•Caused by Neisseria meningitidis, a gram negative diplococcus
- What are the different serotypes (strains) of Neisseria meningitidis
•Serotypes A,B,C, Y, W135
- Where is the serotype A of Neisseria meningitidis predominantly found?
• Serotype A associated with large outbreaks in Sahel region of Africa – Meningitis belt.
- Which serotypes of Neisseria Meningitidis are found in the uk?
Serotype B, C and W135
- Which vaccines have caused a decrease in the serotypes B,C and W135 in the Uk?
MenC and now MenB vaccine.
- What is the range of diseases that Neisseria meningitidis can cause?
•Can cause disease ranging from meningitis to life threatening meningococcal sepsis.
36.What makes meningococcus so effective in sepsis?
- Hexa-acylated Lipid A (more toxic than penta-acylated) and terminal residue mimicry of host antigen (has a very short O antigen component)
- Blebs parts of the membrane that are full of LPS and lipid A component – overwhelming immune response due to this
