Microbial Pathogenesis Flashcards
(21 cards)
What factors influence whether a germ causes disease?
1) Infectious dose
2) Route of transmission
3) Host immunity
What is LD₅₀ and why is it important?
LD₅₀ (Lethal Dose 50%) is the dose required to kill 50% of hosts; it quantifies virulence
What does a high LD₅₀ indicate?
Organism is less virulent (requires more to kill)
What is the trade-off between virulence and transmissibility?
High virulence may kill host quickly, reducing chances for transmission
What happened when Myxoma virus was introduced into the UK?
Rabbit population dropped by 99% due to high mortality
How did Myxoma virus transmission vary by geography?
1) Dry areas (e.g., Australia) poor transmission
2) Wet areas (e.g., Murray Valley) high transmission via mosquitoes
What are virulence grades of Myxoma virus and their effects?
1) Grade I - High virulence, fast death
2) Grade III - Lesions but rabbits survive
3) Grade IV-V - Mild, self-limiting infection
Why did the virulence of Myxoma virus decrease over time?
Evolution favoured strains that allowed better transmission, rabbits also developed resistance
What are examples of innate barriers to infection?
1) Skin
2) Mucus
3) Stomach acid
4) Mucociliary clearance
5) Normal flora
How can host factors affect disease outcome?
1) Genetics
2) Nutrition
3) Immunity
4) Lifestyle influence susceptibility and severity
What are bacterial ‘weapons’ or virulence factors?
1) Capsules
2) Adhesins
3) Enzymes
4) Toxins
5) Modulins
6) Siderophores
7) Motility
What functions do bacterial virulence factors perform?
1) Adhere to host
2) Evade immunity
3) Damage tissue
4) Acquire nutrients
What is an exotoxin?
A protein secreted by bacteria causing specific damage to the host
What is an endotoxin?
Lipopolysaccharide (LPS) from Gram- bacteria’s outer membrane (released when damaged), causes systemic inflammation
What diseases are caused by secreted bacterial toxins?
1) Tetanus
2) Botulism
3) Diphtheria
4) Scarlet fever
5) Cholera
6) Whooping cough
What is ribosylation in the context of bacterial toxins?
Addition of ADP-ribose to host proteins, altering their function (e.g., diphtheria toxin)
What are some immune evasion strategies used by bacteria?
1) Serum resistance
2) Hiding inside cells
3) Blocking phagocytosis
4) Quorum sensing
5) Manipulating apoptosis
What is quorum sensing?
Bacterial communication that coordinates gene expression based on population density
Why is iron acquisition important for bacteria?
Iron is essential but limited in host, needed for bacterial growth
What are siderophores?
Molecules secreted by bacteria to scavenge iron from environment
How does Vibrio cholerae overcome mucus barriers?
By secreting Hap mucinase which degrades mucus layer for access to epithelial cells
