Micro-organisms and their application

• Aseptic technique


  • Prevents contamination of work and environment when working with micro-organisms
• Growing bacteria and fungi on nutrient agar in a Petri dish

  1. Sterilise Petri dishes and nutrient agar before pouring agar

  2. Use inoculating loop to transfer bacteria, sterilise before and after use

  3. Only lift Petri dish lid slightly to prevent contamination

  4. Secure lid with adhesive tape, label and date

  5. Incubate at 25°C for 24-48 hrs

  6. Sterilise plates and equipment after use
• Colony


  Growth from a single bacterium, indicates number in original sample
• 20-200 colonies on each plate is a reliable number to count
• More than 200 colonies are likely to be clumping together, making it difficult to identify individual colonies
• Fewer than 20 colonies is not a reliable number to count
• Growing Penicillium fungus in a fermenter to produce Penicillin


  1. Provide optimum pH, temperature, oxygen, nutrients

  2. Organism grows and secretes antibiotic into medium

  3. Culture medium removed, filtered, penicillin extracted
• Fermenter apparatus


  • Acid/alkali reservoir to control pH
  • Water jacket to control temperature
  • Air diffuser to bubble air through culture
  • Paddles to stir culture
• Room temperature


  Bacterial growth is uncontrolled and rapid
• Refrigerator


  Slows bacterial growth
• Freezer


  Stops bacterial growth