Antibiotics

Question 1

Describe selective toxicity

Answer 1

Selective toxicity is the ability to damage the infecting organism without damaging the host.

• Early treatments for infectious diseases (such as syphylis) involved the use of highly toxic ‘medicines’ more harmful than the actual diseases

Question 2

Describe how antibiotics work by targeting key bacterial components

Answer 2

Penicillin:
- 1928: Alexander Fleming observed that colonies of the bacterium Staphylococcus bacteria could be destroyed by the mould Penicillium notatum.
- Penicillin works by interfering with the normal formation of the bacterial cell wall (by inhibiting the formation of peptidoglycan cross-links)
- Different classes of antibiotics target different bacterial cell wall components (but we just need to know the bacterial cell wall synthesis affecting ones)

Question 3

How do bacteria become resistant to antibiotics?

Answer 3

• Selection of mutants: Mutations are an important cause of genetic diversity in microbial populations
  - A portion of the bacterial population gains resistance to Antibiotic X by mutation. Some bacteria with the resistance survive
  - Bacteria with resistance multiply, passing on the resistant trait. Resistant bacterial populations survive subsequent encounters with Antibiotic X
• Beta Lactamase: Enzyme produced by bacteria and used to destroy penicillin

Question 4

Describe how gene transfer helps pass on antibiotic resistance

Answer 4

Horizontal gene transfer:
- Some bacteria gain resistance by acquiring genes from external sources, this can occur through: transduction, transformation, conjugation
- Bacteria with the resistance survive Antibiotic X
- Bacteria with resistance multiply, passing on resistant trait
- Resistant bacterial populations survive subsequent encounters with Antibiotic X

Vertical gene transfer:
- A portion of the bacterial population gains resistance to Antibiotic X by mutation. Some bacteria with the resistance survive
- Bacteria with resistance multiply, passing on the resistant trait. Resistant bacterial populations survive subsequent encounters with Antibiotic X

Question 5

How do we reduce the development of antibiotic resistance

Answer 5

• Decrease antibiotic utilisation
  Reduce infections and outbreaks through improved hygiene and infrastructure, restrict use in agriculture
• Improve diagnostics
  New methods to identify resistant bacteria can make treatment more effective, and reduce outbreaks.
• Identify new targets
  Some cellular pathways are harder for bacteria to bypass or modify, making them ideal targets for new antibiotics.
• Combination therapies
  Traditional antibiotics can be combined with molecules that block resistant mechanisms