microbiology

• aseptic technique

  • flame neck of jar containing bacteria with Bunsen burner before and after collecting sample
  • sterilise disposable pipette with ethanol then collect 1cm cubed of the bacteria
  • lift lid of petri dish at an angle but not fully open to drop bacteria on here open it in the direction of the Bunsen flame
  • sterilise glass spreader by dipping in ethanol then flaming and spread bacteria - seal petri dish with four pieces of tape
  • incubate at max 25 degrees to prevent harmful growth
• preparation

  • wipe down bench with disinfectant spray
  • wash hands with antibacterial hand wash
  • heath agar plate to high temps to kill bacteria
• effect of antibiotics on growth step 1

  use sharpie to mark out three areas on bottom of plate and label these with each antibiotic you will be using
• effect of antibiotics on growth step 2

  soak three paper disks in different antibiotics and one control disk in water. Once you have placed your bacteria cultures put each disk in its corresponding section. Incubate the plate over night in an incubator set to 25 degrees face down to prevent condensation and sealed.
• effect of antibiotics on growth step 3

  A zone of inhibition should have formed around the antibiotic where non-resistant bacteria have been killed. Measure the diameter of the zones - the bigger the zone the more effective the antibiotic.
• number of bacteria in a population

  bacteria at the end of growth period = bacteria at the beginning of growth period x 2 to the power of number of divisions
• culturing microorganisms

  • bacteria are grown in culture medium which contains all it needs to grow e.g. agar jelly
  • hot agar poured into shallow petri dish and left to cool and set
  • inoculating loops, sterile dropping pipettes and spreader used to transfer microorganisms to the culture medium
• independent variable

  • type of antibacterial or antibiotic used
• control variable

  • temp of incubation
  • concentration and volume of antiseptics/antibiotics
  • duration of incubation
  • size of Petri dish used
• Dependant variable

  Diameter of zone of inhibition