Microbiology Required Practical 2

• What is the aim of the microbiology investigation described?

  To investigate the effect of different antiseptics or antibiotics on bacterial growth
• What equipment is needed for the microbiology investigation?

  • Agar plate
  • Heatproof mat
  • Fiber paper discs
  • Three antiseptics (e.g., mouthwash, TCP, antiseptic cream)
  • Disinfectant bench spray
  • 1% Virkon disinfectant
  • Antibacterial handwash
  • Forceps
  • Clear tape
  • Hand wash
  • Wax pencil or permanent marker
  • Incubator set to 25°C
• What is the first step in the method for the microbiology investigation?

  Spray the bench with disinfectant and wipe dry with paper towels
• Where should you mark the agar plate?

  On the bottom of the agar plate, not the lid
• What should be marked on the agar plate?

  • 3 segments
  • A dot in the middle of each segment
  • Your initials, date, and name of bacteria
• What should you do after marking the agar plate?

  Wash your hands with antibacterial handwash
• How should the antiseptics be applied to the agar plate?

  Place them onto different filter paper discs
• How should the lid of the agar plate be handled when placing the filter paper discs?

  Lift the lid at an angle carefully
• What should be done after placing the filter paper discs on the agar plate?

  Tape the lid onto the agar plate securely
• At what temperature should the agar plate be incubated?

  25°C
• How long should the agar plate be incubated?

  48 hours
• How should the diameter of the clear zones be measured?

  Using a ruler and taking a second measurement at 90 degrees
• What should be done with the lid while measuring the clear zones?

  Do not remove the lid
• How should the results of the investigation be recorded?

  • In a table format
  • Include type of antiseptic
  • Diameter of clear zone in mm
  • Mean diameter
• What is the purpose of repeating the procedure with different concentrations of the same antiseptic?

  To investigate the optimum concentration of antiseptic used to kill bacteria
• What safety precautions should be taken during the experiment?

  • Wear safety goggles when handling Virkon disinfectant
  • Wash hands before and after handling bacteria
• What are some sources of error in the experiment?

  • Irregular shape of the clear zone
  • Difficulty in determining the width
  • Possible contamination from other bacteria