Antibiotics and Resistance

Question 1

Define antibiotic.

Answer 1

Usually produced naturally by a bacterium or a fungus against bacteria in a classic sense

Question 2

Define prophylaxis.

Answer 2

Use of antimicrobial drugs to prevent an infection

Question 2

Define antimicrobial drug.

Answer 2

Has a high level of selective toxicity (toxic to microbes but has no or little toxicity to human or host cells)

Question 2

Define chemotherapy.

Answer 2

Use of antimicrobial drugs for treatment of a disease.

Question 3

Define spectrum of activity.

Answer 3

Range of bacterial types that an antibiotic targets
- Narrow vs broad spectrum

Question 4

Define antiseptics.

Answer 4

More toxic to microbes than to host cells
- Topical uses

Question 5

Define disinfectants.

Answer 5

Has a low selective toxicity
- Can cause damage to both mi robes and host cells

Question 6

Explain how antiseptics and disinfectants differ from antibiotics.

Answer 6

Antibiotics have more selective toxicity than antiseptics and disinfectants

Question 7

List the three major sources of antimicrobial drugs.

Answer 7

1. Natural
2. Semisynthetic
3. Synthetic

Question 8

Define selective toxicity.

Answer 8

Toxic to microbes but not toxic (or little) to human/host cells

Question 9

Describe strategies to design an antimicrobal drug with high
selectivity.

Answer 9

• Differential targets: cellular or metabiotic targets present in bacteria but not in human cells
• Differential dose tolerance: bacteria more sensitive to a drug than human cells

Question 10

Identify the five antibacterial drug targets.

Answer 10

1. Peptidoglycan
2. 70S ribosome
3. Folic acid synthesis
4. DNA/RNA synthesis
5. Plasma membrane

Question 11

For each antimicrobial drug target, give at least one drug and describe the drug’s antibacterial action.

Answer 11

1. Peptidoglycan
   - Penicillin: inhibits cross-linking of glycan molecules
   - Vancomycin: inhibits peptidoglycan elongation
2. 70S ribosome
   - Tetracycline: binds to 30S subunit of ribosome (blocks attachments of charged aminoacyl-tRNA so new amino acids can’t bind to peptide chain)
3. Folic acid synthesis
   - Sulfa drugs: inhibit dihydropteroate synthetase (bacteria can’t use pre-formed folic acid but human cells can)
4. DNA/RNA synthesis
   - Fluoroquinolones: inhibition of the activity of bacterial DNA gyrase and topoisomerase
   - Metronidazole: activated by bacterial flavodoxiin
   - Rifampin: inhibition of the activity of bacterial DNA-dependent RNA polymerase
5. Plasma membrane
   - Polymyxin B: binds to the LPS of the outer membrane and makes the membrane permeable (for Gram-negative bacteria)

Question 12

Explain why effective drugs against viral, fungal, protozoan, and helminthic infections are much limited.

Answer 12

Lack of differential targets
- Viruses use human cells to replicate
- Fungi/protozoa/helminths are eukaryotes just like humans

Question 13

Explain the importance of drug susceptibility test.

Question 14

Define minimal inhibitory concentration (MIC) and explain how it is determined for a drug.

Answer 14

Concentration where growth is absent

Question 15

Define minimal bactericidal concentration (MBC) and explain how it is determined for a drug.

Answer 15

Concentration needed to kill bacteria

Question 16

Define bactericidal drug and bacteriostatic drug.

Answer 16

• Bactericidal: kills bacteria
• Bacteriostatic: inhibits bacterial growth

Question 17

Design a simple experiment to determine whether an antibiotic is bactericidal or bacteriostatic. Discuss factors that may influence the interpretation of your experimental data.