Pathogens

Question 1

Virulence

Answer 1

• measure of pathogenicity
• can be quantified by establishing experimental metrics such as median lethal dose number of bacteria needed to kill 50% of a subject population and medial lethal time, time taken to kill 50% of a subject population
• virulence factors can help bacteria to
  1) invade the host
  2) cause disease
  3) evade host defences or treatment

Question 2

What are virulence factors

Answer 2

• often complex structures or activities
• components often encoded together in pathogenicity island - coordinated expression
• only expressed under certain conditions
• often initiated by a single specific stimuli
• virulence factors are molecules by pathogens that add to their effectiveness and help them to achieve their purpose.

Question 3

Examples of virulence factors?

Answer 3

• capsule surrounding the bacterial cell, protection from phagocytosis
• mechanism to adhere to cells or surfaces
• mechanism to invade cells eg type 3 secretion system
• endotoxins - the lipopolysaccharide of gram negative bacteria
• exotoxins - proteins / enzymes produced or secreted by some bacteria

Question 4

virulence factors - focus on adhesion

Answer 4

• cell-surface component or appendage that facilitated adhesion to surfaces or other cells in order to
  1) penetrate external cell
  2) secrete enzyme / toxin into external cell
  3) affect host cell immune receptors
• often first step in initiation of infection
• demonstrates species or tissue tropism
• binds to specific receptors on external cell surfaces
• typically fimbriae and surface polysaccharides