Culturing Microorganisms

• What can be investigated using cultures of bacteria grown in labs?

  The effect of disinfectants and antibiotics
• How often can some species of bacteria multiply under optimal conditions?

  Once every 20 minutes
• What do bacteria require to multiply quickly?

  An adequate supply of nutrients and appropriate temperature
• What nutrients do bacteria need for growth?

  Carbohydrates, proteins, minerals, and vitamins
• What temperature promotes faster bacterial growth?

  Warmer temperatures
• What is the maximum allowed temperature for bacterial growth in a school lab?

  25°C
• What happens if the temperature exceeds 25°C in a lab?

  More harmful pathogens are likely to grow
• In what two forms can bacteria be grown in the lab?

  In nutrient broth solution or on agar gel plate
• What are the conditions required for optimal bacterial growth?

  • Adequate supply of nutrients:
  • Carbohydrates
  • Proteins
  • Minerals
  • Vitamins
  • Appropriate temperature (maximum 25°C)
• What is an important aseptic technique regarding the bunsen burner?

  Work should be done in front of a lit bunsen burner
• Why is a bunsen burner used during aseptic techniques?

  It creates a convection current to prevent contamination
• What should be done to agar jelly before pouring it into a petri dish?

  It should be heated to kill microorganisms
• What is the purpose of cooling and setting hot agar jelly?

  To allow it to solidify for culture
• What is done to an inoculating loop before transferring bacteria?

  It is passed through a hot flame
• Why is the inoculating loop heated before use?

  To kill any microorganisms on the loop
• How should petri dishes be handled to minimize contamination?

  They should be opened as little as possible
• What is the purpose of securing the lid of a petri dish with tape?

  To prevent condensation from dropping onto agar
• What is the maximum incubation temperature for cultures in a school lab?

  25°C
• Why should cultures not be incubated above 25°C?

  To restrict the growth of harmful pathogens
• How does the use of a bunsen burner contribute to aseptic techniques?

  It prevents airborne contamination through convection currents
• What is the inhibition zone?

  An area where no bacterial growth has occurred; the larger the zone, the more effective the substance tested is against the bacteria
• What’s the equation to work out the zone of inhibition?

  Area = Pi x Radius squared
• How do you calculate bacteria in population?

  • The average amount of time it takes for a bacterial cell in a population to divide is the mean division time
  • The number of times a cell has divided and how many cells it produces can be determined if you know the mean division time and how long division has been occurring
• What’s the aim of this practical?

  To investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and zones of inhibition
• What is the procedure of this practical?

  • Use an aseptic technique to place filter paper discs soaked in different antiseptics/antibiotics onto uncontaminated agar platescontaining bacteria
  • Measure the zone of inhibition around the growing colonies of bacteria to compare the effect of different antiseptics/antibiotics
  • Calculate the area of each zone
• What is the purpose of prepared Petri dish plates in this practical?

  To investigate bacterial growth
• Why is it important to use good microbial aseptic techniques?

  To prevent contamination in microbiology investigations
• What is vital to ensure in microbiology investigations regarding antiseptics or antibiotics?

  Only the effect on bacterial species is investigated
• What is the ideal temperature for bacterial growth in school?

  25 °C
• Why is maintaining an ideal temperature important in bacterial growth?

  To reduce chances of growing harmful pathogens
• Which bacterial cultures are most likely used in this practical?

  Safe strains of coli or Micrococcus luteus
• What should be included in the experimental design for this practical?

  A control group
• What should one of the paper discs on the bacterial agar plate contain?

  Sterile water instead of antiseptic or antibiotic
• Why is it important to use sterile water on one paper disc?

  To attribute differences in growth to antiseptic or antibiotic
• How does using a control group enhance the validity of the experiment?

  It allows comparison to isolate effects of treatments
• What are commercially produced antibiotic discs used for?

  They replace soaking discs in disinfectants
• What process allows bacteria in agar to multiply during incubation?

  Binary fission
• How can the multiplication of bacteria be visually identified in agar?

  By agar darkening or colonies appearing
• What happens to antiseptics in the antibiotic discs during the experiment?

  They diffuse into the agar
• How does the concentration of antiseptics change with distance from the disc?

  It decreases with distance from the disc