Bailey- Antibiotics

Question 0

What are the characteristics of an ideal antibiotic? (4)

Answer 0

1 Broad spectrum of activity
2 Would not induce resistance
3 High therapeutic index
4 Selective toxicity

Question 1

What are the 2 modes of action antibiotics can have?

Answer 1

Bactericidal

Bacteriostatic

Question 2

What is therapeutic index?

Answer 2

Toxic does: effective dose

Ideally you want this ratio high. 1 would result in death to the bacteria but also toxic to the human

Question 3

What are 4 ways to achieve selective toxicity for microbes?

Answer 3

1 unique cell wall
2 enzymes for replication, translation and transcription
3 unique essential metabolites
4 unique ribosome structure

Question 4

How can antibiotics inhibit bacteria? (5)

Answer 4

1 Inhibition of cell wall synthasis
2 Disruption of cell membrane function
3 inhibition of protein synthsis
4 inhibition of nucleic acid synthesis
5 Act as antimetabolites

Question 5

How do antibiotics inhibit cell wall synthesis?

Answer 5

• prevent formation of peptidoglycan
• prevent AA side chains from binding
• prevent strands from elongation
• prevent peptide bond formation
• prevent transfer from cytoplasm to periplasmic space

Question 6

How does penicillin disrupt cell wall synthesis?

Answer 6

Wins substrate competition with gram +/- bacteria and it becomes cleaved instead of the subterminal d-ala needed to become active. This is also toxic to the bacteria

Question 7

What do all penicillins have in common?

Answer 7

B-lactam ring structure (variable side chains)

Question 8

What do antibiotics use to disrupt cell membrane function?

Answer 8

With polymxin B sulfate

-disrupts cell membrane by binding to phospholipids and displacing LPS (similar structure to LPS)

Question 9

What is the most common way for antibiotics to inhibit bacteria?

Answer 9

Inhibition of protein synthesis

Question 10

T/F: The bacterial ribosome is different from human?

Answer 10

True. Bacteria is small in size

Question 11

How do antibiotics block the ribosome cycle?

Answer 11

• Prevent ribosomal subunits from binding (30s & 50s)
• inhibit tRNAs
• inactive the ribosome
• prevent the ribosome from recognizing the start site
• disrupt formation

Question 12

What antibiotic inhibits tRNA?

Answer 12

Tetracyclines

Question 13

What antibiotic prevents ribosomal subunit formation?

Answer 13

Linezoid

Question 14

What antibiotic inactivates ribosomes?

Answer 14

Amniogylcosides

Question 15

What antibiotics prevents recognition of the start site on the ribosome?

Answer 15

Macrolides chloramphenicol

Question 16

This antibiotic inhibits DNA replication and is NOT toxic to us

Answer 16

Metronidazole- becuz it’s converted from Inert to active by anaerobic microbes (inhibiting nucleic acid synthesis)

Question 17

2 antibiotics that affect DNA gyrase

Answer 17

Nalidixic acid
Quinolones
(Both inhibit translation; nucleic acid synthesis)

Question 18

An antibiotic that inhibits RNA polymerase

Answer 18

Rifamycin (prevents translation; nucleic acid synthesis)

Question 19

Bacteria need PABA to react with a precursor to form folic acid to form essential AAs. This antibiotic blocks that. What mechanism is this?

Answer 19

Sulfides, specifically sulfanilamide.

Action as antimetabolites

Question 20

Why does antibiotic resistance occur?

Answer 20

Selective pressure extended by antibiotics.

Overuse of antibiotics (agriculture, physicians, pharmacists, and patient misuse)

Question 21

What are the 3 steps in the action of antibiotics? (This is consistent with Where drug resistance can occur)

Answer 21

1. Drug penetrates the envelope
2. Transport into the cell
3. Drug binds to target

Question 22

What are 3 mechanisms of drug resistance?

Answer 22

1. Synthesis of enzymes that inactive the drug
2. Prevention of access to the target site
3. Modification of the target site

Question 23

How can bacteria synthesize enzymes to inactivate penicillins?

Answer 23

Break the B-lactamase bond

Question 24

2 ways to prevent access to the target site?

Answer 24

1. Change the porins that many antibiotics enter the cell through (resistance to tetracyclines and quinolones) 2. Develop efflux pumps to pump the antibiotics out of them (tetracycline resistance)

Question 25

2 ways to modify the target site?

Answer 25

1. Modify the enzyme affinity | 2. Alter the metabolic pathway (ie change the PABA precursor penicillin competes with)

Question 26

What are 3 ways antibiotics resistance can be spread?

Answer 26

1. Chromosomal associated resistance 2. Plasmid mediated resistance 3. Rapid spread of resistance

Question 27

Why is it important to finish the entire dose of antibiotics?

Answer 27

Bacterial sensitivity to antibiotics occurs over a dynamic range. (Quit them too soon selecting for the least sensitive/resistant bacteria)

Question 28

How do you combat an antibiotic resistant pathogen? With examples

Answer 28

- synergism ie penicillin and streptomycin - antagonism ie penicillin and chloramphenicol - indifferent

Question 29

What are the drawbacks to administrating an antibiotic cocktail?

Answer 29

- failure to eliminate the pathogen can lead to a superinfection - synergistic toxicity

Question 30

Are antibiotics effective against all microbes?

Answer 30

No- ie not viruses