Lecture 9: Antimicrobials

Question 1

What is an antibiotic?

Answer 1

“Chemical produced by a microorganism that kills or inhibits the growth of another organism”

Question 2

What is an antimicrobial agent?

Answer 2

“Chemical that kills or inhibits the growth of microorganisms”

Question 3

What are the possible antibacterial results?

Answer 3

1. Bactericidal: kills bacteria

2. Bacteriostatic: inhibits growth and reproduction

Question 4

What are the structural classes of antibiotics

Answer 4

1. Beta-Lactam antibiotics
2. Glycopeptide antibiotics
3. Tetracyclin antibiotics
4. Aminoglycoside antibiotics
5. Macrolide antibiotics

Question 5

How do antibiotics work? what is their target and mechanism of action?

Answer 5

1. Cell Wall synthesis:
   a. Beta Lactams (penicillins,
   cephalosporins, carbapenems,
   monobacams)
   b. Vancomycin Bacitracin
2. Nucleic acid/DNA synthesis:
   a. DNA gyrase - quinolones
   b. RNA polymerase - rifampin
3. Protein wall synthesis
   a. 30s ribosome subunit - tetracyclines,
   aminoglycosides
   b. 50s ribosome subunit - macrolides,
   clindamycin, linezolid,
   chloramphenicol, streptogramins
4. Metabolic enzymes
   a. Folate synthesis - sulfonamides,
   trimethroprim
5. Cell membrane - polymyxins

Question 6

How can bacteria be antibiotic resistant?

Answer 6

1. Impermeable cell envelope
2. Target modification - altering the
   drugs target
3. Antibiotic modification - inactivating
   the antibiotic
4. Efflux employs genes coding for
   enzymes that actively pump antibiotic
   out

Question 7

what type of antibiotic is penicillin

Answer 7

beta-lactam

Question 8

How does penicillin function?

Answer 8

1. Affects cell wall synthesis
2. Targets transpeptidases (used in
   reforming bonds between molecules
   in peptidoglycan)

Question 9

How is it penicillin can bind to transpeptidases active site?

Answer 9

Due to its structure resembling D-Ala-D-Ala

Question 10

What is the resistance mechanism against penicillin

Answer 10

1. Antibiotic modification/inactivation

2. Penicillinase (beta-Lactamase)

Question 11

How does penicillinase work?

Answer 11

1. Deactivation of penicillin by hydrolysing the beta-lactam ring
2. results in penicilloic acid

Question 12

How do we counteract penicillinase/beta-lactamases?

Answer 12

1. “Clavulanic acid”
   a. Amoxicillin
   b. Augmentin
2. binds to beta-lactamases with higher
   affinity
3. inhibits action