beta lactam antibiotics and vancomycin Flashcards
Why is the bacterial cell wall a drug target?
because humans don’t have cell walls. The formation of cell walls are prevented rather than the destruction of made cell walls because they are very tough so its easier to prevent their synthesis
What are the main structural differences between gram positive and gram negative cell walls?
+ve: thick peptidoglycan layer, techoic acids
-ve: thin peptidoglycan layer, outer membrane layer
What is the function of the cell wall?
- to maintain cell shape
- to protect the membrane from rupturing as osmotic pressure is high inside the cell meaning high salt conc, therefore high water conc
Give an example of norcardiform bacteria and why are they difficult to stain?
mycobacteria = TB
They are gram +ve but are difficult to stain because the peptidoglycan layer is covalently attached to the polysaccharide arabinogalactan which lipids are esterified into making up 60% of the cell wall. Lipids are almost resistant to staining and to antibiotics and biocides.
What do peptidoglycan consist of?
repeating disaccharide units of 2 different N-acetylated amino sugars.
short peptide chains are attached to alternate amino sugars and these cross link via peptide bonds (cross links are species dependent)
Give 2 examples of enzymes that act on cell wall synthesis
transpeptidase and carboxypeptidase (they cleave the b lactic ring)
What are the three groups of beta lactic antibiotics?
penicillins, cephalosporins, carbapenems (all have a beta lactic ring)
What factors do beta lactams need to have in order to be effective?
- must be able to penetrate the cell wall
- should be resistant to beta lactamases (produced by bacteria causing resistance)
- resistant to stomach acid (to ensure they don’t break down)
Give 3 examples of semi synthetic penicillins:
ampicillin (sensitive to B lactamase degradation), amoxicillin, methicillin and flucloxacillin (last 2 resistant to all B lacatmases which is good)
Why is penicillin given IV?
as it is acid labile
What are first, second and third generation cephalosporins?
1st: rarely used
2nd: gram -ve activity, given orally
3rd: gram -ve activity, IV, used for serious illness
Give 2 examples of cephalosporins:
Cefaclor (2nd gen) and ceftriaxone (3rd gen)
What are 2 advantages of carbapenems and give an example?
- very broad spectrum
- resistant to most beta lactamases
e. g. imipenem
What are monobactams resistant against?
gram negative (only 1 monobactam - aztreonam)
What is vancomycin?
- non ribosomal peptide (very difficult to synthesise)
- glycosolated with many unusual amino acids
- inhibits cell wall synthesis by preventing cross link formation
- given IV
