IMMUNOLOGY - Antibiotic Action

Question 1

What is selective toxicity?

Answer 1

An agent which harms the invading organism without harming the host

Question 2

Define bactericidal antibiotics

Answer 2

Antibiotics which kill the bacteria

Question 3

Define bacteriostatic antibiotics

Answer 3

Antibiotics which inhibit the growth of bacteria. This action is reversible

Question 4

Which category of antibiotics target peptidoglycan within the bacterial cell wall?

Answer 4

β-lactams

Question 5

Give three examples of β-lactam drugs classes

Answer 5

• Penicillin
• Cephalosporin
• Monobactam

Question 6

How do β-lactam drugs kill bacteria?

Answer 6

β-lactam drugs inhibit the action of transpeptidase enzymes which cross-link the peptide bonds between the NAG-NAM dimers that make up the peptidoglycan layer of the cell wall. This occurs during bacterial replication causing the bacteria to lose its structure and rigidity and eventually bulge and lyse due to the bacteria’s high internal oncotic pressure

Question 7

How is penicillin G and penicillin V administered?

Answer 7

Penicillin G is administered via the parenteral route and penicillin V is administered orally

Question 8

What are the benefits of ampicillin and amoxicillin drugs compared to penicillin?

Answer 8

• Target G+ and more G- bacteria than penicillin
• Parenteral AND oral administration

Question 9

What is the advantage of using methicillin drugs?

Answer 9

Targets G+ bacteria including β-lactamase producing bacteria

Question 10

What are the main drug classes which disrupt bacteria protein synthesis?

Answer 10

• Aminoglycosides
• Chloramphenicol
• Tetracyclines
• Macrolides and Lincosamides

Question 11

What is unique about aminoglycoside drugs compared with other drug classes which disrupt bacteria protein synthesis?

Answer 11

Aminoglycosides are bactericidal

Question 12

How do aminoglycoside drugs inhibit protein synthesis in bacteria?

Answer 12

Aminoglycosides inhibit the initiation of translation

Question 13

How do chloramphenicol drugs inhibit protein synthesis in bacteria?

Answer 13

Inhibit the enzyme peptidase transferase which is involved in forming peptide bonds between the amino acids of the developing protein

Question 14

How do macrolide and lincosamide drugs inhibit protein synthesis in bacteria?

Answer 14

1. Inhibit the enzyme peptidase transferase which is involved in forming peptide bonds between the amino acids of the developing protein OR Inhibit translocation of the ribosome along the mRNA

Question 15

How do tetracycline drugs inhibit protein synthesis in bacteria?

Answer 15

Block the ‘A’ site, preventing the binding of tRNA to the mRNA

Question 16

What are the main drug classes which inhibit the biosynthesis of folic acid in bacteria?

Answer 16

• Sulphomanides
• Trimethoprim

Question 17

Why is folic acid biosynthesis essential for bacteria to survive?

Answer 17

Folic acid is requires for 1-carbon metabolism (which is required for nucleic acid synthesis). Bacteria have to carry out folic acid biosynthesis as unlike vertebrates, bacteria cannot gain folate as a vitamin and instead have to synthesis their own

Question 18

Which enzyme involved in folic acid biosynthesis is inhibited by sulphomanide drugs?

Answer 18

Dihydropteroate synthase (DHPS)

Question 19

Which enzyme involved in folic acid biosynthesis is inhibited by trimethoprim drugs?

Answer 19

Dihydrofolate reductase (DHFR)

Question 20

Sulphonamide drugs and trimethoprim drugs are often clinically used together. What is the collective term for these drugs?

Answer 20

Potentiated sulphonamides

Question 21

(T/F) Sulphonamides and trimethoprim drugs are chemically made

Answer 21

TRUE

Question 22

What is the main drug class which inhibits DNA replication in bacteria?

Answer 22

4-fluoroquinolones

Question 23

Give an example of one of the most commonly used 4-fluroquinolones

Answer 23

Enrofloxacin

Question 24

How do 4-fluoroquinolone drugs inhibit DNA replication in bacteria?

Answer 24

Inhibition of topoisomerase enzymes involved in coiling bacterial DNA

Question 25

What is the main drug class that damages bacterial DNA?

Answer 25

Nitromidazoles

Question 26

Give an example of a nitromidazole drug

Answer 26

Metronidazole

Question 27

What is a unique feature of selective toxicity in nitromidazoles?

Answer 27

Nitromidazoles need to be reduced within anaerobic bacteria in order to activate and cause DNA damage, ultimately killing the bacteria (bacteriacidal)

Question 28

(T/F) The use of metronidazole is prohibited in food-producing animals

Answer 28

TRUE. The use of metronidazole in animals has proven to be genotoxic, carcinogenic and mutagenic

Question 29

What is the main class of drugs which disrupts the cytoplasmic membrane of Gram negative bacteria?

Answer 29

Polymyxins

Question 30

What is the main class of drugs which disrupts the cytoplasmic membrane of Gram positive bacteria?

Answer 30

Depatomycin

Question 31

Sometimes different antibiotics need to be given at the same time. Describe the different possible interactions between antibiotics

Answer 31

Synergism: combined antibiotics have a greater effect
Antagonism: combined antibiotics have a negative effect on one another
Indifferent: combined antibiotics have no effect on one another