5. Staph aureus & MRSA

Question 1

How would staph aureus appear on a gram stain?

Answer 1

Gram positive clusters

Question 2

What antibiotic would you used to treat skin and soft tissue staph.aureus infections?

Answer 2

Flucloxacillin

Question 3

What is MRSA?

Answer 3

Meticillin-resistant staphylococcus aureus

Question 4

What protein does MRSA produce, how does this induce resistance?

Answer 4

Penicillin binding protein 2a, gives resistance to beta lactate antibiotics.

Question 5

What antibiotic is used to treat MRSA?

Answer 5

Vancomycin

Question 6

What type of antibiotic is vancomycin?

Answer 6

Glycopeptide

Question 7

What process do glycopeptide antibiotics target?

Answer 7

Inhibit peptidoglycan cell wall formation by binding to amino acids

Question 8

How can staph aureus be categorised?

Answer 8

Coagulase +ve

Coagulase -ve

Question 9

What does coagulase exotoxin do?

Answer 9

Catalyses fibrinogen -> fibrin, forming clots within the plasma.

Question 10

What virulence factors do staph aureus possess?

Answer 10

Cell wall - polysaccharide capsule, protein A

Cytolytic exotoxins - leukocidin, haemolysins, superantigens (Toxic shock syndrome toxin (TSST))

Question 11

What is a typical feature of a staph aureus infection?

Answer 11

Abscess formation

Question 12

How do staph aureus cause abscess formation?

Answer 12

• Rapid influx of neutrophils
• lyse neutrophils and RBC’s in infected area
• Lysed neutrophils pour out lysosomal enzymes which damage surrounding tissue

Question 13

Where is clostridium difficile usually found in the body?

Answer 13

Large intestine- part of the normal gut flora

Question 14

When can c.diff become pathological?

Answer 14

Overgrow in the colon of an individual on antibiotics that deplete the normal flora.

Question 15

What is a risk factor for a c.diff infection?

Answer 15

Recent or current course of antibiotics

Question 16

What toxins does C.diff produce?

Answer 16

Toxin A and B

Question 17

What does Toxin A do?

Answer 17

Enterotoxin - excessive fluid secretion, stimulates inflammatory response

Question 18

What does Toxin B do?

Answer 18

Cytotoxin - disrupts protein synthesis, disorganisation of cytoskeleton

Question 19

How would you identify C.diff on a gram stain?

Answer 19

Gram positive rod

Question 20

How would you manage and treat a patient with c.diff infection?

Answer 20

1. Isolate patient
2. Stop all other antibiotics
3. Replace fluid and electrolytes
4. Stop opioids (constipation, prevents clearance)
5. Stop steroid and other immunosuppressants
6. Stop PPI’s - acid aids killing of bacteria

Question 21

What antibiotics would you use to treat mild C.diff infection?

Answer 21

Metronidazole

Question 22

What antibiotics would you use to treat severe C.diff infection?

Answer 22

Vancomycin