2: culturing microorganisms

• 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 in a bacterial culture?

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

  A plate containing nutrient broth in jelly form
• 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?

  By passing it through a flame
• Why do we attach the lid of the agar plate with adhesive tape?

  To prevent contamination from microorganisms
• 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
• Why do we open a sterile agar gel plate near a Bunsen burner flame?

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

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

  Area where bacteria do not grow around antibiotics
• How do we measure the effect of antibiotics?

  By calculating the area of the zone of inhibition
• What is the formula to 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
• Why do we use the value of PI as 3.14 in calculations?

  It is a common approximation for calculations
• 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 passing through flame
  3. Transfer bacteria using the loop
  4. Attach lid with adhesive tape
  5. Incubate agar plate upside down at 25°C
• What are the steps to investigate the effect of antibiotics on bacterial growth?

  1. Clean the bench with disinfectant
  2. Sterilize inoculating loop by passing through flame
  3. Open sterile agar plate near Bunsen burner flame
  4. Spread bacteria evenly over the plate
  5. Place sterile antibiotic disks on the plate
  6. Incubate at 25°C and observe results
• What factors affect bacterial growth in cultures?

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