Required Practical 2: Culturing Microorganisms

• In the diagram we can see a bacterial culture, where bacteria is growing in a nutrient broth solution that contains all of the nutrients needed for bacterial growth and division. The broth is cloudy because it contains a very large number of bacteria.

  
• Another way to culture bacteria is to use an agar gel plate which also contains nutrient broth. In this diagram the broth is set into a jelly using a chemical called agar. The jelly is then poured into a petri dish, in which the bacteria may form colonies.

  
• The sterilisation of petri dishes kills any unwanted microorganisms and prevents contamination.
• Bacteria are normally transferred into the culture using an inoculating loop which is also sterilised by passing it through a Bunsen burner flame
• The lid of a petri dish is attached using adhesive tape in order to stop the lid from falling off and unwanted microorganisms entering.
• The agar plate is placed into an incubator upside down in order to stop moisture from dripping down onto the bacteria and disrupting the colonies.
• Bacteria is normally incubated at 25 degrees Celsius in schools. This reduces the chances that harmful bacteria will grow.
• The steps towards culturing bacteria include:

  1. Sterilise all petri dishes, bacterial nutrient broth and agar
  2. Attach lid of petri dish using adhesive tape
  3. The agar plate is then placed upside down into an incubator
• A workbench is cleaned with disinfectant solution in order to kill microorganisms that could contaminate our culture.
• Sterile agar gel plates are opened near a Bunsen burner flame due to the flame killing bacteria in the air.
• To find out the effect of antibiotics on bacterial growth:

  1. Clean the bench with disinfectant solution
  2. Sterilise an inoculating loop
  3. Open a sterile agar gel plate near a Bunsen burner flame
  4. Use the loop to spread the chosen bacteria evenly over the plate
  5. Place sterile filter paper discs containing antibiotic onto the plate
  6. Incubate the plate at 25 degrees Celsius
• Around the antibiotic discs, we have a region where the bacteria have not grown, called the zone of inhibition.

  
• In order to calculate the zone of inhibition, we calculate the area of the circle that is covered by the bacteria
• Aseptic technique is a set of practices that protects patients from healthcare-associated infections and protects healthcare workers from contact with blood, body fluid and body tissue.

  Examples include:

  • Not growing microorganisms at body temperature.
  • Using sterile loops when transferring cultures.
  • Sterilising or disposing of all used equipment.
  • Washing hands thoroughly