Principles of Antimicrobial Chemotherapy

Question 1

Define chemotherapy.

Answer 1

The use of chemicals, natural or synthetic, to inhibit the growth and replication of invading organisms or cancer cells within the body.

Question 2

Define selective toxicity.

Answer 2

1- Agents which are toxic to invading organisms or cancerous cells, but relatively harmless to the host of normal cells
2- This approach depends on the existence of biochemical differences between target cells and host cells

Question 3

What five drug classes are active against the cell membrane?

Answer 3

1- β-lactam and cephalosporin
2- Glycopeptide
3- Cyclic peptide
4- Phosphonic acids
5- Lipopeptide

Question 4

What drug class is penicillin G?

Answer 4

β-lactam

Question 5

Where are peptidoglycans found?

Answer 5

1- Cell walls

2- Do not occur in eukaryotes

Question 6

Describe the features of peptidoglycans.

Answer 6

1- Strands are made of of multiples of amino-sugars: N-acetylglucosamine and N-acetylmuramic acid dimers.
2- N-acetylmuramic acid has a short peptide side chain
3- Peptide side chains cross-link to form a latticework which provides strength
4- Found in bacteria cell walls

Question 7

How do β-lactams, such as penicillin G, act on bacteria?

Answer 7

Prevent peptidoglycan cross-linking in cell wall

Question 8

What are the two first generation penicillins?

Answer 8

1- Penicillin G

2- Penicillin V

Question 9

What are the five β-lactamase-resistant penicillins?

Answer 9

1- Methicillin
2- Oxacillin
3- Nafcillin
4- Cloxacillin
5- Dicloxacillin

Question 10

What are two broad-spectrum penicillins?

Answer 10

1- Ampicillin

2- Amoxicillin

Question 11

What are four extended-spectrum penicillins?

Answer 11

1- Carbenicillin
2- Ticaracillin
3- Azlocillin
4- Piperacillin

Question 12

Where are cephalosporins derived from?

Answer 12

From the fungus Cephalosporium acremonium

Question 13

What is the mechanism of cephalosporins?

Answer 13

Prevent cross-linking of peptidoglycans in cell wall

Question 14

What is cephalexin?

Answer 14

1- Cephalosporin

2- Oral intake

Question 15

What is cefuroxime?

Answer 15

1- Cephalosporin

2- Parenteral intake

Question 16

What is cefotaxime?

Answer 16

1- Cephalosporin

2- Parenteral intake

Question 17

What are two examples of antibiotics that inhibit the folate pathway in bacteria?

Answer 17

1- Sulphonamides

2- Trimethoprim

Question 18

What is the mechanism of sulphonamides?

Answer 18

1- Selective toxicity
2- Inhibit folate pathway in bacteria
3- Inhibit dihydropteroate synthetase enzyme

Question 19

What is the mechanism of trimethoprim?

Answer 19

1- Selective toxicity
2- Inhibits folate pathway in bacteria
3- Inhibits dihydrofolate reductase enzyme

Question 20

What are four examples of aminoglycosides?

Answer 20

1- Streptomycin
2- Kanamycin
3- Neomycin
4- Gentamycin

Question 21

What is the mechanism of aminglycosides?

Answer 21

1- Form ionic bonds at the cell surface
2- Penetrate cell wall and cell membrane
3- Diffuse into cytoplasm
4- Bind to bacterial ribosomes either at the interface between the assembled 30s and 50s subunits or directly to individual subunits
5- Inhibit protein synthesis by causing ribosomes to misread mRNA

Question 22

What is the mechanism of tetracyclines?

Answer 22

1- Prevent attachment of tRNA to A site on the mRNA-ribosomal complex
2- This prevents the addition of new amino acids to the growing peptide chain

Question 23

What determines the difference in activity between different tetracyclines?

Answer 23

What determines the difference in activity between different tetracyclines?

Question 24

What is the mechanism of chloramphenicol?

Answer 24

1- Binds to ribosomes
2- Prevents addition of new amino acids to growing peptide chain
3- Prevents association of peptidyl-transferase to amino acid, thus preventing formation of peptide bond

Question 25

What is the mechanism of erythromycin?

Answer 25

1- Binds to ribosomes
2- Prevents addition of new amino acids to growing peptide chain
3- Prevents translocation of ribosomes down the mRNA chain

Question 26

What is the mechanism of clindamycin?

Answer 26

1- Binds to ribosomes
2- Prevents addition of new amino acids to growing peptide chain
3- Prevents association of peptidyl-transferase to amino acid, thus peptide bond cannot be formed

Question 27

Where are fluoroquinolones derived from?

Answer 27

Synthetically

Question 28

What are three examples of broad-spectrum fluoroquinolones?

Answer 28

1- Ciprofloxacin
2- Ofloxacin
3- Norfloxacin

Question 29

What are two examples of narrow-spectrum fluoroquinolones?

Answer 29

1- Cinoxacin

2- Nalidixic acid

Question 30

What is the mechanism of fluoroquinolones?

Answer 30

1- Inhibit bacteria DNA Topoisomerase II (DNA gyrase)

2- Transcription and translation not carried out