Staphylococcus Aureus

Question 1

Why is staphylococcus aureus significant?

Answer 1

800000 NZers infected asymptomatically at any time
75000 of those will get skin infections because of it
600 develop invasive disease
50 will die
Responsible for majority of hospital acquired infections

Question 2

What is the origin of staph A?

Answer 2

Predominantly a human pathogen but humans can transfer it to domestic animals. Peak incidence is in first year of life from mother to child. If infected it will reside in the nose

Question 3

What are the five components of SA virulence?

Answer 3

1. Adherence (techoic acids and cell wall proteins)
2. Invasion (hyaluronidase/lipases/fibrinolysins)
3. Immune evasion (avoids phagocytosis)
4. Toxins (lethal to a variety of cell types)
5. Superantigens (inhibits adaptive immunity and can cause toxic shock syndrome)

Question 4

Which conditions can SA cause?

Answer 4

Food poisoning
Skin and soft tissue infections (most common)
Bone and joint infections
Endocarditis
Deep organ abscess
Bacteraemia

Question 5

What are some ways that SA avoid the immune system?

Answer 5

Release a leukotoxin to destroy neutrophils
Release CHIPs to interfere with chemotaxis
Coated with a capsule to prevent antibody binding
Protein A binds the heavy chain of antibodies
Catalase inactivates H2O2, which neutrophils use to kill bacteria

Question 6

How is SA treated?

Answer 6

1. Stabilise patient
2. Drain pus
3. Antibiotics used to disrupt the cell wall

Question 7

What makes SA difficult to treat?

Answer 7

There is no vaccine and no clear evidence on whether preventative decolonisation works
It quickly becomes resistant to antibiotics (most SA is now resistant to methicillin)