culturing microorganisms

• Preparing uncontaminated bacterial culture using aseptic technique

  1. Sterilize petri dishes, bacterial nutrient broth, and agar to kill unwanted microorganisms

  2. Transfer bacteria using a sterilized inoculating loop

  3. Seal plate with adhesive tape to prevent contamination

  4. Incubate plate upside down at 25°C to prevent moisture disrupting colonies
• Investigating effect of antibiotics on bacterial growth

  1. Clean bench with disinfectant

  2. Sterilize inoculation loop

  3. Spread chosen bacteria evenly on sterile agar plate near Bunsen burner flame

  4. Place sterile filter paper discs containing antibiotics on plate

  5. Incubate plate at 25°C

  6. Measure zone of inhibition around antibiotic discs to calculate area using formula: Area = π x r^2
• Bacteria can double in number every 20 minutes with enough nutrients and suitable temperature
• Nutrient broth


  Solution containing all the nutrients bacteria need to grow and divide
• Agar gel plate


  Nutrient broth gelled using a chemical called agar, allows bacteria to grow into visible colonies
• Contamination from other microorganisms in the environment must be avoided when culturing bacteria
• Zone of inhibition


  Region around antibiotic disc where bacteria do not grow