Required practical 2: culturing microorganisms

• Aseptic technique

  • Sterilize petri dishes, bacterial nutrient broth, and agar
  • Sterilize inoculating loop by passing through flame
  • Attach lid with adhesive tape to prevent contamination
  • Incubate agar plate upside down at 25°C to prevent moisture dripping down
• Investigating effect of antibiotics on bacterial growth

  1. Clean bench with disinfectant

  2. Sterilize inoculation loop

  3. Open sterile agar plate near Bunsen burner flame

  4. Use loop to spread bacteria evenly over plate

  5. Place sterile filter paper disks containing antibiotics onto plate

  6. Incubate plate at 25°C

  7. Measure zone of inhibition around antibiotic disks
• Zone of inhibition

  Region where bacteria are not growing around antibiotic disk
• Calculating area of zone of inhibition

  Area = π x R^2, where R is the radius of the zone of inhibition
• Bacteria can double in number every 20 minutes with enough nutrients and suitable temperature
• Agar gel plates contain nutrient broth gelled using a chemical called agar
• Agar plates allow bacteria to grow into visible colonies
• Incubating at 25°C reduces the chances of harmful bacteria growing