CMB1003/L09 Host-Pathogen Interactions Flashcards
What is pathogenicity, or virulence factors?
Structures, molecules or regulatory systems that enable the disease process
What drives pathogenicity?
Adhesion to epithelial surface or invasion of underlying tissue
What must bacteria to do to become a pathogen?
Get into a place where they shouldn’t be
Approximately how many pathogens make up the microbiome?
10^13
How can pathogens adhere to mucosal surfaces? (2)
Subvert host cell function (extracellular)
Invade underlying tissue (invasive)
What is the role of polysaccharide capsules on pathogens? (3)
Physical barriers to desiccation
Immune masks
Aid adherence
What is the role of the bacterial capsule?
Encases bacterial cell
Provided resistance against immune recognition, phagocytosis & complement killing
Precursor to biofilm formation
Cell surface appendages promote initial interactions with which surfaces?
Host tissues
Medical devices e.g., catheters
Abiotic surfaces in industry
What do structures offer to pathogens? (4)
Physical defence
Nutrition
Intercellular communication
Exchange of genetic material
Describe the 4 stages of biofilm formation.
Adsorption
Irreversible attachment
Growth and division
Mature macrocolony
What is the likely default mode of growth for bacteria in nature?
Biofilms
What are fimbriae capped by?
Sugar-binding, lectin-like proteins
Describe type 1 fimbriae. (2)
CUP type adhesin
Found widely in Gram -ves
What does FimH have a specific affinity for?
Mannose
How are pili different from fimbriae? (3)
Pili are longer, less abundant and involved in genetic exchange
Describe the fimbrial catch-bond theory. (3)
Mechanistic benefit in natural environments subject to fluid shear stress
Strength of binding dictated by an allosteric switch in the FimH-sugar interaction
Can be chemically inhibited
What are the two general pathways of transport across the IM?
SEC - unfolded, common
TAT - folded, elusive substances
What does the SEC pathway of transport across the IM facilitate?
Insertion of proteins into the IM
What do 2 step systems in Gram -ves generally follow?
SEC translocation to periplasm followed by specific system for OM transport
Describe a type 3 secretion system (T3SS). (2)
Required for epithelial attachment (EHEC)
In some cases invasion
Describe a type 6 secretion system (T6SS). (2)
Used for inter-bacterial warfare and host-cell subversion
Describe a type 4 secretion system (T4SS).
Primarily involved in genetic exchange (conjugation)
Where is the damage usually located by bacterial toxins?
Distal to site of infection
What advantages do toxins offer to bacteria?
Access to tissue and nutrients
Facilitating transmission
Enhancing other virulence processes
What 3 mechanisms of action do exotoxins facilitate?
Cytolytic
Disruptive
Stimulatory
Give an example of a cytolytic exotoxin.
Hemolysin
Alpha-toxin
Give an example of a disruptive exotoxin.
AB toxins
Give an example of a stimulatory toxin.
Superantigens
Describe the repressive effect of Stx-phage. (2)
On T3SS
Stimulates cell receptor expression in host
What are endotoxins?
Cell-bound lipopolysaccharides of Gram -ve bacteria
When are endotoxins released?
When cells lyse
What can endotoxin release induce? (2)
Fever, tissue inflammation, diarrhoea
How does the toxicity of endotoxins compare to exotoxins?
Endotoxins far less toxic
What are pathogenicity islands?
Portions of DNA that encode toxins and secretion systems
