Culturing Microorganisms

• Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature
• Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate
• Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics
• The process of binary fission is:

  • The genetic material stored in the plasmids gets replicated
  • The cell starts to expand and the plasmids move to the opposite poles of the cell
  • The cytoplasm divides and cell walls form around the 2 identical daughter cells .
  • Each daughter cell will contain a copy of the DNA and a variable number of plasmids
• Mean division time is the average time it takes for one bacterial cell to divide once
• Mean division time can be used to work out how many times a cell has divided, and therefore the number of cells produced
• Number of divisions = time spent dividing / mean division time
• Number of cells produced = 2^Number of divisions
• Aseptic techniques:

  • Wash your hands and work surfaces
  • Growth media must be heated before use
  • Growth media must be added to a sterile petri dish
  • All work should be done in the presence of a Bunsen burner on a yellow flame to prevent a convection current above the bench and prevent contamination from the air
  • The Bunsen burner can also be used to sterilise equipment such as an inoculating loop
  • The lid of the Petri dish must be taped on
  • The Petri dish must be stored upside down
  • The dish should be incubates at 25C