Infection: Staphylococcus Aureus

Question 1

What is the classification of staph aureus?

Answer 1

Gram positive cocci (appears under the microscope in clusters)

Question 2

What are some common infections caused by staph aureus?

Answer 2

Skin infections eg cellulitis, abscesses
Infections of the respiratory tract eg sinusitis, pneumonia
Food poisoning
Sepsis from bacteraemia due to surgery, catheters, IV lines etc

Common hospital acquired infection

Question 3

Where on the body is staph aureus normally found?

Answer 3

Staph aureus is a commensal on the skin, nose and the respiratory tract

Question 4

What is the coagulase test and how it is useful clinically?

Answer 4

Coagulase is an enzyme that converts fibrinogen in plasma to fibrin clots.
Only staph aureus is coagulase positive, all other staphylococcal species are coagulase negative

Question 5

What are some of the virulence factors of staph aureus?

Answer 5

• produces coagulase enzyme which causes clotting of fibrin which coats the bacterial cell preventing phagocytosis
• secretes exotoxins

Question 6

How are staph aureus infections investigated?

For each investigation what would you expect to see?

Answer 6

Gram staining:
Gram positive cocci in clusters

Coagulase test:
Only positive in staph aureus (negative in all other staph infections)

Question 7

How are staph aureus infections treated?

Answer 7

Flucloxacillin usually used

May be combined with co-amoxiclav for severe infections such as endocarditis.