microbial pathogenesis Flashcards
What is microbial pathogenesis?
The study of the mechanisms by which microorganisms cause disease
Includes gene expression during infection, pathogenicity islands, and virulence factors.
Define infection.
A bacterium capable of disease becomes established in the body.
What is the difference between infection and disease?
Infection is the establishment of a bacterium, while disease is an infection that produces symptoms.
What does colonisation/asymptomatic carriage mean?
Persistence of bacteria in a body site without causing disease.
Define virulence.
The ability of a bacterium to cause infection.
What is a virulence factor?
A bacterial product that contributes to virulence/pathogenicity.
List the categories of virulence factors.
- Products that promote bacterial colonisation and invasion of the host
- Products that cause damage to the host.
What are Koch’s postulates?
- Bacterium should be found in all people with the disease
- Bacterium or products should be found in parts of the body affected by the disease
- Bacterium should be isolated from lesions of an infected person and be maintained in pure culture
- Pure culture should produce symptoms of disease when inoculated into susceptible volunteer or experimental animal
- Same bacterium should be re-isolated in pure culture from intentionally infected animal or human.
What is the molecular version of Koch’s postulates?
- Gene/gene product found in strains of bacteria that cause disease and not in avirulent bacteria
- Disrupting gene in a virulent strain should reduce virulence
- Introducing cloned gene into avirulent strain should render the strain virulent.
Define pathogenicity islands (PI).
Chromosomal clusters of virulence genes found in some pathogenic organisms.
What is the significance of the G+C content in pathogenicity islands?
It is usually different from the remainder of the genome, indicating an extraneous origin.
What are adhesins?
Factors that promote adherence to a host surface.
What role do adhesins play in the disease process?
They are often crucial for achieving an infectious dose.
What are invasins?
Factors that promote invasion of the pathogen into a host cell.
Classify exotoxins.
- Superantigens
- Membrane disrupting toxins
- A-B toxins.
What are superantigens?
Toxins that elicit cytokine production by T cells.
What is the function of cholera toxin?
Triggers massive efflux of chlorine ions, leading to watery diarrhoea.
What are endotoxins?
Lipid-A fraction of the LPS layer in Gram-negative bacteria.
What are the effects of low concentrations of endotoxins?
Fever, complement activation, stimulation of B-lymphocytes.
What are the effects of high concentrations of endotoxins?
Shock and death.
Fill in the blank: Koch’s postulates were formulated in the ______.
1800s.
True or False: Virulence factors only promote bacterial colonization.
False.
What is the role of iron in microbial pathogenesis?
Essential for iron-dependent enzymes in virtually all pathogens.
What are some examples of siderophores synthesized by Gram-negative bacteria?
- Enterochelin
- Aerobactin
- Vibriobactin
- Pyoverdine.
