Preparation of uncontaminated culture use aseptic technique

• Bacteria can multiply once every 20 minutes if enough nutrients are available and the temperature is suitable
• Ways bacteria can be grown

  • Nutrient broth solution
  • Colonies on an agar gel plate
• Nutrient broth solution contains all nutrients required for bacteria to grow including nitrogen for protein synthesis, carbohydrates for energy and other minerals
• Purpose of uncontaminated cultures of microorganisms

  Investigating disinfectant and antibiotic action
• Petri dishes and culture media must be sterilised before use to kill any bacteria already present
• Inoculating loops must be sterilised by passing them through a Bunsen burner flame to kill any bacteria present on the loop
• The Petri dish lid must be secured with tape and the whole dish stored upside down to stop bacteria in the air contaminating the culture and prevent condensation from forming and dripping down onto the colonies
• Cultures are incubated at 25oC in school laboratories because harmful pathogens are less likely to grow at this temperature
• 1

  Use pre-sterilised plastic Petri dishes or sterilise glass Petri dishes and agar gel before using with an autoclave.
• 2

  Pour the sterile agar gel into the Petri dish and allow time to set.
• 3

  Sterilise the inoculating loop by passing it through a Bunsen burner flame.
• 4

  Dip the inoculating loop into the solution of _ and make streaks with the loop on the surface of the agar.
• 5

  Put the lid on the Petri dish and secure it with tape. Label accordingly then turn and store upside down.
• 6

  Incubate the culture at 25oC in school laboratories.