Microbiology

• Method


  1. Spray the bench you are working on with disinfectant then wipe dry with paper towels

  2. On the bottom of the agar plate (not the lid) mark with a wax pencil / permanent marker: 3 segments, a dot in the middle of each segment, your initials, date, name of bacteria

  3. Wash your hands with antibacterial handwash

  4. Place the different antiseptics onto different filter paper discs

  5. Lift the lid of the agar plate at an angle carefully and use forceps to place each filter paper disc onto the dots. Note down the antiseptic applied to each zone

  6. Tape the lid onto the agar plate securely, but loosely enough that oxygen can still reach the bacteria

  7. Place the agar plate in the incubator at 25°C for 48 hours

  8. Measure the diameter of the clear zones after 48 hours using a ruler. Take a second measurement at 90 degrees from your first measurement and take a mean for the diameter. Do not remove the lid when taking measurements

  9. Record the results in a table
• What technique is used to prepare uncontaminated bacterial cultures?

  Aseptic technique
• What should you be able to describe by the end of the video?

  Preparing uncontaminated cultures and antibiotic effects
• How do bacteria reproduce?

  By binary fission
• How often can bacteria double in number with enough nutrients?

  Every 20 minutes
• What is a nutrient broth solution used for?

  To grow and divide bacteria
• Why is the broth cloudy?

  It contains a large number of bacteria
• What is an agar gel plate?

  A petri dish with nutrient broth gel
• What is the purpose of sterilizing petri dishes and nutrient broth?

  To kill unwanted microorganisms
• How is bacteria transferred into the culture?

  Using an inoculating loop
• How do you sterilize an inoculating loop?

  Pass it through a flame
• Why do we attach the lid of the petri dish with adhesive tape?

  To prevent contamination
• At what temperature do we normally incubate bacteria in schools?

  25 degrees Celsius
• Why do we incubate agar plates upside down?

  To prevent moisture from disrupting colonies
• What is the first step in investigating the effect of antibiotics on bacterial growth?

  Clean the bench with disinfectant
• What does the flame do when opening a sterile agar gel plate?

  Kills bacteria in the air
• What do we place on the agar plate to test antibiotics?

  Sterile filter paper disks
• What is the zone of inhibition?

  Area where bacteria do not grow
• How do you calculate the area of the zone of inhibition?

  Area = PI × R squared
• If the radius of the zone of inhibition is 12 mm, what is the area?

  452.45 square mm
• What is the value of PI used in calculations?

  3.14
• What are the steps to prepare an uncontaminated bacterial culture using aseptic technique?

  1. Sterilize petri dishes and nutrient broth
  2. Sterilize inoculating loop by flame
  3. Transfer bacteria using the loop
  4. Seal the dish with adhesive tape
  5. Incubate upside down at 25 degrees Celsius
• What are the steps to investigate the effect of antibiotics on bacterial growth?

  1. Clean the bench with disinfectant
  2. Sterilize inoculating loop by flame
  3. Open sterile agar plate near flame
  4. Spread bacteria evenly over the plate
  5. Place antibiotic disks on the plate
  6. Incubate at 25 degrees Celsius
• What are the key components of a bacterial culture experiment?

  • Nutrient broth solution
  • Agar gel plates
  • Aseptic technique
  • Antibiotic disks
  • Zone of inhibition measurement
• What factors affect bacterial growth in cultures?

  • Nutrient availability
  • Temperature
  • Aseptic conditions
  • Presence of antibiotics