culturing microorganisms

• Culture medium

  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Ways to grow microorganisms in the lab

  • In nutrient broth solution
  • On agar plates
• Culturing microorganisms

  • Microorganisms are very small, so scientists need to grow many of them in the lab using nutrients
• Components of culture medium

  • Carbohydrates for energy
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in nutrient broth

  1. Make a suspension of bacteria and mix with sterile nutrient broth

  2. Stopper flask with cotton wool to prevent air contamination

  3. Shake regularly to provide oxygen
• Growing microorganisms on agar gel plate

  1. Pour hot sterilised agar jelly into a sterilised Petri dish and let it cool and set

  2. Use inoculating loops to spread bacteria over the agar evenly

  3. Tape on lid and incubate for a few days
• Petri dishes and culture media must be sterilised before use
• Inoculating loops must be sterilised by passing through a flame
• Petri dish lid should be sealed but not completely to allow oxygen
• Petri dish should be stored upside down to prevent condensation
• Culture should be incubated at 25 degrees to prevent growth of harmful bacteria
• Testing antibiotic effectiveness

  1. Soak paper discs in different antibiotics and place on agar plate with bacteria

  2. Leave plate for 2 days at 25 degrees

  3. Measure size of inhibition zone around discs
• Inhibition zone

  The clear area left when bacteria die around an antibiotic disc
• To calculate cross-sectional areas, use the formula πr^2