Staph. Aureus

Question 1

Microscopy of S. Aureus

Answer 1

Thick peptidoglycan cells wall

Diveides in multiple planes resulting in clump formation

Question 2

Epidemiology

Answer 2

Ubiquitous
Common cause of disease
Common cause of hospital acquired infections
Common cause of death

Question 3

SA virulence- five factors

Answer 3

1. Adherence
2. Invasion
3. Immune evasion
4. Toxins
5. Superantigens

Question 4

Adherence of SA

Answer 4

Techoic acids provide for rigidity of the cell wall and increase adherence to mucosal surfaces
Cell wall proteins bind to nasal epithelium and fibrogen and collagen fibres

Question 5

Invasion

Answer 5

Secretes enzymes that break down the extracellular matrix, subcutaneous fat (lipases), fibrinolysis (break down fibrin clots that form in response to infection)

Question 6

Immune evasion

Answer 6

• Releases catalase that inactivates the hydrogen peroxide secreted by neutrophils.
• Avoids antibody binding through the presence of a capsule- decreases opsonisation, direct neutralisation, agglutination.
• Interferes with neutrophil chemotaxis through releasing CHIPS (chemotactic inhibitory protein)
• Secretes leukotoxins which destroy neutrophils

Question 7

Toxins

Answer 7

Releases toxins lethal to a number of cell types through forming pores in cells

Question 8

Superantigen

Answer 8

This causes MHC 2 molecules on APC to bind with Helper T cells without regulation- results in excessive T cell activity and consequently ‘cytokine storm’. Inhibits adaptive immunity.

Question 9

Where does SA come from?

Answer 9

Predominantly a human pathogen.