Lecture 37: Antimicrobial Chemotherapy

Question 1

Selective Toxicity:

Answer 1

• Antibiotics highly effective against microbes, no harm to humans

Question 2

Penicillin was found to be ______ by Alexander Fleming.

Answer 2

• Antimicrobial

Question 3

Penicillin became commercialised during _____ _____ __. It was the first antibiotic to be industrialised.

Answer 3

• World War 2

Question 4

What are antibiotics?

Answer 4

• Substance produced by a microorganism that is antagonistic to the growth of other microorganisms in high dilution

Question 5

Antibacterials:

Answer 5

• Act against bacteria

Question 6

Antimicrobials:

Answer 6

• Act against bacteria, virus, fungi, protozoa

Question 7

Three different effects of antibiotics on bacterial cell:

Answer 7

• Bacteriostatic: Stops bacteria reproducing / growing
• Bactericidal: Kills bacteria (they’re still there just dead)
• Bacteriolytic: Kills bacteria and makes it disappear (total cell count goes down)

Question 8

The zone inhibition tells us..

Answer 8

• How effective the antibiotic is

- Free space around the antibiotic

Question 9

One way to test for antibiotic sensitivity is to use an…

Answer 9

• Etest

Question 10

Targets for antibacterials:

Answer 10

• Cell Wall - Penicillin
• Cytoplasmic Membrane - Polymyxins (dodgy, not as selective)
• Protein synthesis - Tetracycline (used widely)
• Metabolic pathway - Sulphonamides
• DNA synthesis - Actinomycin
• RNA synthesis - Rifampin

Question 11

Tetrapeptides join sugar molecules together. This is how a bacteria is synthesised. Antibiotics inhibit cross linking from occurring….

Answer 11

• Transglycosylation

- Transpeptidase

Question 12

In a sealed cave, can antibiotic resistance occur?

Answer 12

• YES

- Antibiotic resistance is a natural occurence

Question 13

Mechanisms of antibiotic resistance:

Answer 13

• Lactam ring gives penicillin it’s function to inhibit transpeptidase
• Antibiotic resistance bacteria have developed an enzyme to destroy that ring
• Change porins to decrease antibiotic uptake (gram negative bacteria)
• Antibiotic gets pumped out of bacteria

Question 14

Mechanisms of antibiotic resistance (G):

Answer 14

• Original resistance genes arise by mutation

- Antibiotic rich environment gives antibiotic resistant mutants a selective advantage

Question 15

How to prevent antibiotic resistance developing

Answer 15

• Test antibiotic sensitivity of target microorganism
• Use sufficiently high concentration of antibiotic
• Treat for reasonable period
• Complete therapeutic regime
• If chronic infection = treat with a combination of antibiotics
• Avoid adding antibiotics to animal foods (or Kiwifruit)

Question 16

Choice of Antibiotics:

Answer 16

- Influenced by:
Nature of infection (gram + or - ) 
Source of infection (community/hospital)
Resistance
Site of infection

Question 17

Side effects to Antibiotics:

Answer 17

• Toxicity
• Allergies
• Damage to normal microbiota
• Resistance development