Lecture 6.3: Antibiotics 3 Flashcards
Name the 5 targets of antimicrobial agents.
Cell wall: Beta lactams, glycopeptides.
Cytoplasmic membrane
Ribosomes: Aminoglycosides, chloramphenicol.
Nucleic acid: Rifamycines, quinolones.
Folic acid.
What is the main acid used for cross linked bridges in a peptidoglycan wall?
N-acetyle muramic acid.
What is the mechanism of action of vancomycin? What are its limitations?
It is an antibiotic that interferes with the two D-ala’s which are kind of like the glue in a peptidoglycan wall. Thereby preventing the formation of it.
Cannot work on gram negative bacteria as it is a large molecule, and cannot get through outer membrane.
Why are enterococci are resistant to vancomycin.
Because they have a D-ala-D-lac.
What is VISA. How do they work?
Vancomycin resistant staph aureus. Has a very thick peptidoglycan wall that mops up the vancomycin. We cannot add copious amounts of vancomycin because it is toxic.
How does penicillin G work?
Targets the transpeptidase enzyme of bacteria. This enzyme hydrolyses D-ala. As such, because penicillin binds irreversibly to it, it can no longer produce the cell wall, resulting in autolysis.
This is the reason penicillin is bactericidal.
What is a bacteria’s defence to beta lactams such as penicillins?
They break down penicillin via beta lactamase. They can also harbour a different transpeptidase enzyme that doesn’t bind to penicillin, so penicillin doesn’t work.
What does clavulonic acid do?
Binds irreversibly to beta lacatamase, rendering it useless so penicillin can regain its mechanism of action.
What are aminoglycosides? How do they work?
They essentially insert themselves as an anticodon, replacing it. Could act as a STOP codon.
They work in ribosomes. Example is gentamicin.
What are 3 methods bacteria use to defend against aminoglycosides?
They modify the aminoglycosides so it cannot pass the lipid bilayer.
They pump out amino glycosides (not very effective)
They modify their membrane OR ribosomes so aminoglycosides can’t get through or bind.
