B3 - microbiology

• GROWING BACTERIAL

  1. Make an agar plate
  2. When jelly is cooled, inoculating loops are used to transfer microorganisms to culture medium
  3. Microorganisms then multiply
• Inhibition zone

  The larger the inhibition zone, the more effective the antibiotic is against the bacteria
• Control

  • Paper disc soaked in sterile water
• Difference between growth around control disc and antibiotic disc

  Effect of the antibiotic
• PREVENTING CONTAMINATION

  • Petri dishes and culture medium must be sterilised to kill unwanted bacteria
  • Inoculating loop should be sterilised
  • After transferring bacteria, lid of Petri dish should be lightly tapped to stop microorganisms from air getting in
  • Petri dish should be stored upside down to stop drops of condensation falling onto agar
• • Cultured are incubated at 25 degrees at school labaratories
  • This is because harmful pathogens are more likely to grow above this temperature
• • Bacteria multiply by binary fission as often as 20 minutes if they have enough nutrients and swarm environment
• Binary fission:

  1. Circular DNA and plasmid replicate
  2. Cell gets bigger and circular DNA starnds move to opposite ends of cell
  3. Cytoplasm begins to divide and new cell walls start to form
  4. Cytoplasm divides and two new daughter cells are produced
  5. Each daughter cell hss one copy of circular DNA
• method:

  1. inoculate agar plate with bacteria
  2. work within 20cm of Bunsen Burner flame to sterilise air
  3. incubate agar plate at 25 degrees for few days so bacteria can grow
  4. add three different antibiotics to paper discs
  5. use one paper plate with no antibiotic
  6. divide plate into four sections
  7. open agar plate 20cm near Bunsen burner and add discs
  8. put plate in incubator for 48 hours at 25 degrees
  9. measure radius of blank zones around disc - use formula for area