Staphylococcus aureus

Question 1

Describe the morphological features of staphylococci.

Answer 1

Gram positive cocci in clusters. Colonisers of skin and mucosa.

Question 2

How is staphylococcus aureus differentiated between other staphylococcus species?

Answer 2

S. aureus is a coagulase and DNAse positive, whereas other staphylococci species are not.

Question 3

List some complications of S. aureus infection.

Answer 3

food poisoning, toxic shock syndrome, scalded skin syndrome, skin and soft tissue infection, folliculitis, furuncle, infective endocarditis, osteomyelitis, septic arthritis, pneumonia, epidural abscess.

Question 4

List some surface adhesions of S. aureus.

Answer 4

Clumping factor A, B; fibronectin binding proteins A, B; collagen binding adhesion; protein A.

Question 5

What is the mechanism of action behind toxic shock syndrome from S. aureus infection.

Answer 5

Superantigens such as TSST1 results in non-specific activation of T cells by 20% rather than the normal 0.0001%. This results in a cytokine storm, an overwhelming inflammatory response resulting in endothelial leakage, haemodynamic shock, multi-organ failure, and possibly death.

Question 6

What gene is involved in increased toxin production by S. aureus?

Answer 6

agr gene regulator, the accessory gene regulator, when activated, increases the umber of toxins produced and decreases the number of adhesins, and vice versa.