Lecture 12: Staphylococcus aeureus

Question 1

What conditions can staph aureus lead to?

Answer 1

• Fever and new murmur
• Osteomyelitis
• Skin and soft tissue infection i.e impetigo and folliculitis
• Pneumonia
• Infectious disease outbreak
• Post operative complications

Biggest bacterial threat to adults

Question 2

Whats of note about Staph. Aureus structure?

Answer 2

Thick peptidoglycan cell wall

Question 3

Whats more common meningitis or Staph. aureus sepsis?

Answer 3

Staph. aureus sepsis is significantly higher than meningitis

Question 4

Where is staph. aureus more common?

Answer 4

Low socioeconomic areas. Reflects systemic issues.

Question 5

Where is staph. aureus mainly found in humans?

Answer 5

Up the nose. (colonised) Typically human-human transmission. Largely asymptomatic.

Question 6

Describe how folliculitis occurs;

Answer 6

Bacteria from skin attempt to invade hair follicle and damage cells. The damaged cells release cytokines i.e chemotaxis, increased vascular permeability and vasodilation. (Allows diapedesis, (WBC move thru endo), as well as Cytokines = irritate nerves fibres and pain, swelling, warmth, redness

i.e the red follicle apperance.

Question 7

How is Staph in folliculitis dealt with?

Answer 7

Neutrophils, macrophages etc phagocytose bacteria and kill them with toxins.

Question 8

Why is staph aureus so potent? and examples

Answer 8

It has a range of factors to avoid the immune system.

i.e

Catalse to convert H2O2 released from NK cells.
Protein A to prevent opsonisation / AB function
Can lyse neutrophils with gamma hemolysin
Can interfere with compliment activation

Question 9

How does staph hide itself from the immune system?

Answer 9

1) Coats itself in antibodys, clotting proteins, sugar capsule (avoid detection / phagocytosis as SA hidden)
2) Release chemicals (CHIPS) to prevent chemotaxis
3) Use catalase to breakdown H2O2 inside neutrophils
4) Release toxins i.e hemolysis to destroy neutrophils..

etc etc etc

Question 10

What are the 3 factors of staph aureus treatment?

Answer 10

1. Stabilise the person
2. Drain pus
3. Antibiotics

Question 11

How does penicillin act?

Answer 11

Penicillin inhibits transpeptidase a bacterial enzyme that cross links that sugars of peptidoglycan (and provides structural integrity of the bacterial cell wall) thus PENICILLIN causes bacteria to explode.

Question 12

What is MSRA?

Answer 12

Methicillin resistant staph aureus. The bacteria developed an enzyme to degrade the antibiotic.

Many staph are resistance to penicillin and some to methicillin