Flashcards in Lecture 2 - Bacterial Pathogenesis Deck (63):
Differentiate between pathogens, opportunistic pathogens and normal flora
Pathogens: inherently cause disease
Opportunistic pathogens: only cause disease when given the chance (when host is immunosupressed, antacids etc.)
Normal flora: bacteria that are present in the gut under normal circumstances and do not cause adverse effects
Describe how a bacterium can be normal flora, opportunistic infection as well as a pathogen
It is normally found on the skin - doesn't cause disease.
However, when an individual is immunosupressed, it may cause disease
Toxin production in food can cause intoxication
What is a 'virulent organism'?
This is an organism that is likely to cause disease
What is an 'avirulent organism'?
This is an organism that won't cause disease under normal circumstances (eg. normal physiology)
What are virulence determinants?
Give some examples
Characteristics that make an organism virulent
What are some 'opportunities' for commensals to cause disease?
Immuno compromised individual
Pathogen is moved (site specific)
Why are commensals important?
They contribute to:
- immune system
When does an infection go from asymptomatic to symptomatic?
After replication, when there is damage to host dissue
What is the generalised process of bacterial replication?
Damage to host
Describe how colonisation occurs
What are the two types of colonisation
• surface molecule (binding molecule / adhesin) + host receptor
Fimbrial / non - fimbrial
Why are epithelial cells said to be polarised?
Different ends of the cell have different expression of receptors
Why is polarisation of epithelial cells important?
Bacteria may need to damage epithelium to gain access to receptors
What are the two functions of fimbriae?
What is the structure of fimbriae?
Hollow protein tube
Adhesin on the tip
Which part of a pilus binds to the host cells receptor?
The adhesin on the tip
How do we know fimbriae are involved in colonisation?
• Can be used as antigen in vaccines for immunity
• Infection blocked by antibodies to fimbriae
How does a Urinary tract infection arise?
Bacteria from the rectum 'ascend' to cause an infection in the bladder
Who is more commonly affected by UTIs?
Which bacterium is responsible for UTIs?
Uropathogenic E. coli
How do uropathogenic E. coli cause disease?
1. 'P' fimbrial attachment to bladder epithelium
2. Bacteria internalised
3. Replicate to high levels
What is non-fimbrial adhesion?
This is when bacteria adhere to the host cell with molecules present on their cell wall
• glycocalyces (slime layer, capsule)
• teichoic acids
Give an example of non-fimbrial adhesion
Staphylococcus aureus adheres using Teichoic acids of the cell wall to the fibronectin and collagen of the host
Teichoic acid -- Fibronectin
What are the two forms of glycocalyx?
How may they be differentiated?
Slime layer can be washed away?
What is the function of glycocalyx?
- Evasion of host defences by masking antigens
What is a biofilm?
Any group of microorganisms in which cells stick to each other on a surface
Is penetration required for disease?
some pathogens are extracellular
Describe how bacteria penetrate cells
RME: receptor mediated endocytosis
Invasin or molecule on bacteria binds to a receptor on the host cell --> taken up into the cell
How do bacteria spread between cells?
When bacteria penetrate a cell, they can alter the features of the cell, such an cellular junctions
Tight junctions become more leaky --> bacteria can spread more easily
How does Pseudomonas cause disease, considering that it lacks the ability to invade
It can only invade when there is damage to the epithelium - such as in burns victims
Where are the different locations where bacterial replication can occur?
1. On cells (extracellularly)
What are the pros and cons of the different locations of intracellular bacterial replication?
pro: more protection from molecules in the cytosol
con: less nutrients
and vice versa
True of false: penetration and replication are essential for infectious disease?
Only replication is essential
Bacteria can cause disease extracellularly
Describe the features of the bacterial growth curve
Log phase: exponential growth of bacteria, diving by binary fission
Plateau: stable numbers
Decline: due to competition for resources and quroum sensing
True or false?
There can be many different species of bacteria in a biofilm
Normally not just one species
What do biofilms contain?
These hold the bacteria together
What controls the formation of a biofilm?
What is quorum sensing?
Recognition of bacteria within a colony by chemical signals released by neighbouring bacteria
What happens when there are sufficient numbers of bacteria?
The signal takes effect
What are the two types of signal in quorum sensing?
What are biofilms normally associated with?
What sort of genes do signals from quroum sensing regulate?
What happens to metabolic activity in a biofilm?
Reduced metabolic activity, because the bacteria can rely on their neighbours and become more efficient
Why are microfilms bad?
- Increased expression of virulence determinants
- Protection form host defences
- Greater opportunity for gene transfer
When does an infection pass from subclinical to disease?
Subclinical: numbers below the threshold
Disease: numbers above a certain threshold
How may physical barriers be subverted by bacteria?
How may the complement system by avoided by bacteria?
Enzymes that destroy C'
How do bacteria evade phagocytes?
- Escape phagosome
- Survive in phagosome
- Kill phagocytes
How do bacteria evade Ab?
How do bacteria evade APCs?
Down regulate MHC expression to reduce the efficiency of APCs
What are the three ways that bacteria can cause damage to the host?
In general, how does exotoxin work?
1. Produced by bacteria
2. Gets into host cell (B subunit)
3. Cytotonic, cytotoxinc (A subunit)
When is endotoxin primarily produced?
When cells die
What is the structure of endotoxin?
What is the effect of LPS?
• Activates the alternate complement pathway
• Binds and activates macrophages and neutrophils by PRRs
Describe how bacteria disseminate
Give some examples
1. They produce compounds that break down:
• intercellular matrices
2. Use host physiology
• nervous system
Describe how bacteria can use the host's physiology to disseminate
• intra / extracellular
Why is infection a race? Who are the competitors?
It is a race:
Pathogen vs. Host's immune system
Immune system wins: recovery
Pathogen wins: loss of function, death
Pathogen partially wins: chronic infection, latency
How can we affect the outcome of 'The Race'?
• Maintain physical barriers
• Maintain innate IR
• Maintain adaptive IR
• Reduce virulence of organism
• Reduce n° of organisms
What are some features of normal flora?
• mutualistic relationship with host (don't cause disease)
• cause disease if moved to another area
• occupy the niche to prevent pathogens colonising
• contribute to immune system and metabolism
• Can be transient / stable
TRUE / FALSE:
In Biofilms there is increased:
• metabolic activity
• expression of virulence determinants
• gene transfer
• protection from host and antibiotics
• metabolic activity FALSE
• expression of virulence determinants TRUE
• replication TRUE
• gene transfer TRUE
• protection TRUE
How do bacteria kill phagocytes?
Draw a typical AB5 exotoxin