bacterial host-pathogen interactions Flashcards
What type of date is pathogenic and virulence?
pathogenic = qualitative
virulence = quantitative - differentiates clinical isolates
What is pathogenicity?
ability of an organism to take fold through adhesion by breaking into the mucosa and attaching to the human tissue.
What are the types of adhesion?
Extracellular - subvert host cell function
Invasive - invade underlying tissue during pathogenesis.
Adherence is caused by protein surface structures on the pathogen and they interaction with host cell receptors. Polysaccharide capsules aid adherence and also double up as a physical barrier to desiccation and immune masks.
How is the bacterial capsule a key virulence determinant?
It is a polymer of repeating sugar units that extend upwards with a dynamic structure that encases the bacterial cell. They provide resistance against immune recognition like phagocytosis and complement killing. they act as a mask, hiding the pathogen from the cell surface as sugars are highly antigenic and will not be recognised as a threat, unlike surface proteins.
What is fimbriae mediated adhesion?
Fimbriae are smaller than pili and form specific interactions with host cell receptors. They are capped with a sugar binding, lectin-like protein, helping them blend in.
Type 1 fimbriae are expressed by diff. types E.coli, primarily in pathogenic strains in the urinary tract.
The fimbrial catch-bond theory gives fimbriae a mechanistic benefit in stress environments. The bladder has a lot of stress as urine is constantly flushing through it, the force of this causes the fimbriae structures to extend and stretch, allowing them to bind to the bladder epithelium.
What are bacterial protein secretion systems?
The purpose is to secrete proteins from the inner membrane (IM) to the outside of the cell (OM). The IM will recognise unfolded peptides and shuttle them to periplasmic space where they are folded and transported to the OM.
What is the type 3 secretion system (T3SS)?
Required for epithelial attachment (EHEC) and in some cases invasion, like with salmonella. They are not receptor specific. They extend largely into extracellular space and form specific interactions with host cell membranes. Their purpose is to deliver proteins into the host cell and alter its function.
What is the T6SS?
used for inter-bacterial warfare as well as host-cell subversion. It is like a retractable phage like organism. it has a contractile needle like protein that sits inside the cytoplasm, and has a loading complex sitting across the membrane. The effective proteins are loaded into the system and punctured into the neighbouring cell.
What is the purpose of the T4SS?
primarily involved in genetic exchange (conjugation).
What are exotoxins?
have high toxicity and are secreted by the bacterial cell. They can be destroyed but are typically highly immunogenic. They include neurotoxins and cytotoxins (haemolysin).
AB toxins are disruptive toxins and examples include the Shiga toxin and cholera toxin. They have an A and a B component. The B component finds a target receptor on a host cell.
What are endotoxins?
endogenously produced toxins like lipopolysaccharides. they are poorly immunogenic, protein structures on the surface of bacterial cells that trigger a toxic immune response. they are released when the pathogen dies and cause innate responses like inflammation and diarrhoea.
What are examples of site specific toxins?
Enterotoxins - small intestine leading to fluid loss.
neurotoxins - affect nerve cells e.g. tetanus and botulinum.
Renal toxins e.g. Stx
What is Stx (Shiga toxin)?
EHEC (Enterohemorrhagic Escherichia coli) T3SS is essential for colonisation. Stx is triggered in response to certain stresses, but Stx-phage has a repressive effect on the T3SS whilst also stimulating cell receptor expression in the host.
Stx inhibits protein synthesis in sensitive eukaryotic cells.
