antibiotics on bacteria

• IV


  The type of antibiotic used
• DV


  Zone of inhibition left by antibiotic (area measured in cm²)
• control variables

  • Same concentraton of antibiotic used
  • Type and amount of bacteria used – E.coli will be used as the bacteria and it will be evenly spread across an agar medium
  • Volume of antibiotic used for each disc – mast ring will be used with equal concentrations of each antibiotic
  • Contamination of culture – aseptic techniques and sterile equipment used to avoid contamination of bacteria culture
  • Temperature of cultures – all Petri dishes should be incubated overnight at 25°C
  • pH of medium – an agar jelly will be used in each case with a consistent, neutral pH
• method

  1. Label 2 Petri dishes for the antibiotic mast ring and the distilled water control – include the date.
  2. Use the sterile forceps to place the paper discs of distilled water onto their corresponding Petri dish. Close each dish and seal with hazard tape. Make sure that a small gap is left so that oxygen can enter and there is no build-up of anaerobic bacteria.
  3. Leave the cultures to incubate at 25°C for 24 hours.
  4. Open each Petri dish and use a ruler to work out the zone of inhibition for each paper disc/mast ring section.
• conclusion


  The varying zones of inhibition are caused by the varying effectiveness of each antibiotic. A larger zone of inhibition indicates a greater effectiveness at killing bacteria and this will also depend on the resistance capabilities of the bacteria. Some antibiotics are bactericidal – directly killing bacteria – and some are bacteriostatic – limiting bacteria growth.