Introduction To Antibiotics

Question 1

What Are Antibiotics?

Answer 1

Chemical Compounds which Treat Bacterial
Infections by supplementing body’s Natural
Defenses by killing/inhibiting bacteria

Must be sufficiently Non-Toxic to be given to Infected Host

Question 2

What Are Antibiotics Used For?

Answer 2

• Treating Bacterial Infections
• Infection Prevention
• Prophylaxis Pre-Post Surgery/Trauma
• Agriculture
• Aquaculture

Question 3

What Are The Antibiotic Classifications?

Answer 3

Natural
Produced naturally by Fungi/Bacteria, selectively inhibit growth of others

Semi-Synthetic
Chemically Modified Natural Antibiotics

Totally Synthetic
Manufactured

Question 4

What is SELECTIVE TOXICITY?

Answer 4

Exploiting Differences Between Structure + Metabolism of Infecting Micro-organisms and Host Cells

Question 5

Describe Penicillin.

Answer 5

• The First Broad Spectrum Antibiotic
• Low Toxicity + High Activity
• Inhibited Growth of Staphylococcus
• Produced By Penicillium Fungus

Question 6

What Are the 2 Types of Antibiotics?

Answer 6

Bactericidal: Kill Bacteria

Bacteriostatic: Prevents Division of Bacteria

Question 7

What Are The Spectrums of Antibiotics?

Answer 7

Broad Spectrum:
Kill wide range of Bacteria

Narrow Spectrum:
Kill Specific Type/Group of Bacteria

Question 8

How Do Antibiotics Work?

Answer 8

1. Inhibit Cell Wall Synthesis
   e.g.
   β-lactams, Glycopeptides, Cycloserine,
   Bacitracin
2. Alter Protein Synthesis
3. Alter Nucleic Acid Synthesis
4. Alter metabolism

Question 9

What Are β-Lactam Antibiotics?

Answer 9

• Antibiotics containing β-Lactam ring
• All Have same mode of Action
• Includes Penicillin

Examples:

1. Penicillin V (N)
2. Penicillin G (N)
3. Amoxicillin (SS)
4. Methicillin (SS)

Question 10

How Does penicillin Work?

Answer 10

Aim: Weaken Bacterial Cell Wall

Key Words:

N-Acetylglucosamine (NAG)

N-Acetylmuramic acid (NAM)

Bacterial Cell Wall:

• Contains Peptidoglycan (PG)
• PG: Mesh made of NAM & NAG
• NAM + NAG joined By TRANSPEPTIDASE

Mechanism:

1. β-Lactam Antibiotics block TRANSPEPTIDASE
2. Holes form in chain-link fence
3. Bacteria undergo Lysis
4. Competitive Inhibition, Irreversible Binding

Question 11

How is Antibiotic Sensitivity Tested?

Answer 11

1. Disk Diffusion Assay
2. Grow Bacterial culture to test Antibiotics on
3. Add Antibiotic Discs of Same Diameter
   Containing same Concentration for Different
   Antibiotics
4. Dilutions
5. Dilute Antibiotic to find Lowest
   Concentration needed to Inhibit Bacterial
   Growth/Kill 99.9% of original Bioload

Question 12

Compare Disk Diffusion Assays and Dilutions?

Answer 12

Disk Diffusion Assay

• Simple
• Screen lots of Antibiotics
• Inexpensive
• Qualitative (no info on Antibiotic
  Concentration)

Dilutions

• More Accurate than Disk Diffusion Assay
• Provides Quantitative Data, can modify
  Treatment Regimes
• More Expensive + Labour intensive than Disk
  Diffusion Assay