Antimicrobial Mechanisms Flashcards
What enzyme do B-lactams inhibit, and what does it do?
- blocks transpeptidase
- normally cross-links Muramic acid via their D-ala-D-ala portions (peptidoglycans)
What, on bacteria, does penicillin look like?
D-ala-D-ala
TEM
B-lactamase
TEM TEM TEM
TEM TEM
TEM
What are the glycopeptide antimicrobials?
- Vancomycin
- teicoplanin
What type of bacteria are intrinsically resistant to Vancomycin?
Gram (-) bacteria
What does Vancomycin bind to?
D-ala-D-ala
-Blocks cross-linking reaction
What is the phenotype of vancomycin resistance?
D-ala-D-ala → D-ala-D-lac
What is Vancomycin Intermediate S. aureus (VISA)?
- Characterized by thickening of cell wall.
- Thicker cell wall has more D-ala-D-ala in outer layer of peptidoglycan which can trap vancomycin.
What is cycloserine?
- cell wall synthesis inhibitor
- blocks D-ala ligase
*needs to enter cytoplasm
Which antibiotics inhibits the 30s segment of bacterial ribosomes?
- Aminoglycosides
- Tetracyclines
- Tigecycline
How do aminoglycosides work?
-Bind to 30 S subunit of ribosome and prevent formation of initiation complex
How is bacterial resistance to aminoglycocides mediated?
- Enzymatic inactivation of the drug
- A set of plasmid encoded enzymes can adenylate, phosphorylate or acetylate aminoglycosides
How do tetracyclines work?
Attach to 30 S subunit to prevent binding of incoming aminoacyl-tRNA
How is bacterial resistance to tetracyclines work?
- active efflux of the drug out of the bacteria
- also by a plasmid-encoded tetracycline binding protein
How do macrolides work?
Bind 50S subunit and block translocation.
How do lincosamides work?
Bind 50S subunit and block translocation.
What classes of antibiotics bind the 50s subunit of bacterial ribososmes?
- Macrolides
- Lincosamides
- spectinomycin
- Chloramphenicol
- oxazolidinomes
What is the bacterial mechanism for resistance to macrolides and lincosamides?
-altered target site
How does chloramphenicol work?
- binds 50s subunit of ribosome
- inhibits peptidyl transferase to block peptide bond formation
What is the bacterial mechanism of resistance to chloramphenicol?
-enzymatic inactivation
How do oxazolidinones work?
-Binds 50S subunit and prevents association with 30S subunit
What antibiotic classes inhibit bacterial folic acid metabolism?
- Sulfonamides
- Trimethoprim
How do sulfonamides work?
- inhibit bacterial purine/pryimidine synthesis
- blocks dihydropteroate synthetase
How does trimethoprim work?
- inhibits bacterial purine/pyrimidine synthesis
- inhibits DHFR
