HAI - MRSA

Question 1

S aureus

Answer 1

Staphylococcus aureus - gram positive bacteria
98% of this bacteria is resistant to antibiotics
Commonly found on skin & won’t cause health issues

Question 2

Mechanism of Resistance of S aureus

Answer 2

Target modification mechanism

• The altered target cannot bind to the antibiotic
• S aureus normally produces 4 enzymes call PBPs for cell wall biosynthesis
• PBPs 1-4 can be modified be beta lactic antibiotics resulting in their inhibition and death
• MRSA: altered PBP called PBP2a, which is not inhibited by beta lactam antibiotics, and can perform the same function
• Beta lactamases have low affinities for PBP2a and react at reduced rates
• The active site of PBP2a is closed in absence of its peptidoglycan substrate, preventing access of beta lactam to the critical site serine
• PBP2a has to bind 2 portions of peptidoglycan of the cell wall in grooves on its surface, outside the active site
• binding of first peptidoglycan strand seems to stimulate the opening of the active site (preventing access of all beta lactam)

Question 3

Linezolid - MRSA

Answer 3

Zyvox
Class: Oxazolidinone
Inhibits protein synthesis
Binds to 50S sub particle affecting binding site of tRNA
Gram -ve: resistant by efflux

Question 4

Synercerid- Quinupristin and Dalfopristin -MRSA

Answer 4

IV treatment
Combination inhibits protein synthesis by binding to 70 S ribosome, where both agent bind at the same site
- Both agents: Quinupristin and Dalfopristin
- Bacteriostatic individually
- Bactericidal: together

Question 5

Daptomycin - MRSA

Answer 5

• Lipoprotein
  IV treatment of gram +ve infections
• Binds to cell membrane causing depolarization:
  interrupts ptn, DNA, RNA synthesis

Question 6

Approved Antibiotics - MRSA

Answer 6

Clindamycin, trimethoprim, tetra cycline, ceftobripole, ceftraoline, dalbavacin, oritavancin