Culturing microorganisms

• Bacteria grown on agar plates will form visible colonies on the jelly surface
• In school labs cultures of microorganisms are not kept above 25C as harmful pathogens are more likely to grow
• Investigating effect of antibiotics on bacterial growth

  1. Take petri dish with agar in it. Use an inoculating loop to transfer bacteria onto the agar evenly.
  2. Place paper disks soaked in different types/concentrations of antibiotics on the agar plate. Leave space between disks.
  3. Place a paper disk that has only been soaked in sterile water to use as a control
  4. Leave for 48 hours at 25C
  5. A clear area called an inhibition zone will be left where the bacteria have died. More effective antibiotic is against the bacteria the larger this area will be.
• Petri dishes should be sterilised prior by heating to a high temperature to kill microorganisms
• Inoculating loop should be sterilised prior by passing through a hot flame
• After transferring bacteria, lid of petri dish should be lightly taped on