Antibiotics and Resistance

Question 1

What are the 5 desirable properties of an antimicrobial drug?

Answer 1

1. Selective toxicity
2. Bacteriocidal rather than Bacteriostatic
3. No resistance
4. Not allergenic
5. Soluble, and stable in body fluids

Question 2

Which process are inhibited by antimicrobials?

Answer 2

Cell wall and protein synthesis, Nucleic acid metabolism, membrane function, Enzymatic reactions.

Question 3

What are the 2 origins of resistance?

Answer 3

Innate: All members of a species are resistant due to some specific quality.
Acquired: A strain develops resistance due to a mutation or acquisition of genes.

Question 4

What are the 4 mechanisms of resistance?

Answer 4

1. Exclusion
2. Altered target
3. Bypass
4. Inactivation

Question 5

What is the MOA of Beta lactams?

Answer 5

Block transpeptidation reaction necessary to make PG crosslinks. Targets PBP and requires growing cells to be effective.

Question 6

How does a bacteria become resistant to Beta-lactams?

Answer 6

1. Beta-lactamases

2. Mutations in PBG proteins

Question 7

What is the role of clavulanic acid?

Answer 7

A beta-lactam that acts as a suicide inhibitor of Beta-lactamase.

Question 8

What is the MOA of Vancomycin?

Answer 8

Blocks the release of PG from bactoprenol; Blocking glycan chain extension. Only effective on Gram+

Question 9

What is the MOA of Bacitracin?

Answer 9

Blocks dephosphorylation of bactoprenol pyrophosphate; Only effective on Gram+

Question 10

What is the MOA of polymyxin?

Answer 10

Alters permeability of membranes of Gram- bacteria by interacting with LPS and phospholipids; Polypeptide antibiotic

Question 11

What is the MOA of Daptomycin?

Answer 11

Binds to CM of Gram+ bacteria, depolarizing and disrupting ionic gradient; Lipopeptide antibiotic

Question 12

What are the 3 Mycobacterial cell wall inhibitors?

Answer 12

1. Isoniazid/Ethionamide: Blocks mycolic acid synthesis
2. Ethambutol: Blocks arabinogalactan synthesis
3. Cycloserine: Inhibits alanine synthetase and racemase

Question 13

What is the MOA for Aminoglycosides?

Answer 13

Irreversible inhibition of protein synthesis

Question 14

What is the MOA for Chloramphenicol?

Answer 14

Blocks protein synthesis by inhibiting peptidyl transferase

Question 15

What is the MOA for Oxazolidinones?

Answer 15

Binds P site of ribosome preventing N-formylmethionyl-tRNA from binding; Inhibits protein synthesis.

Question 16

What is the Bacterial resistance to quinolones?

Answer 16

Target site modifications in DNA gyrase/topoisomerase; Porins in CM decrease uptake

Question 17

What is the MOA for metronidazole?

Answer 17

A prodrug that damages bacterial DNA and inhibits DNA repair; Effective against anaerobic bacteria.