PAG 7: microbiological techniques

• what do the areas of the clear zones indicate?

  the larger the clear zone, the more bacteria killed, the more effective the antimicrobial agent
• state the aseptic techniques to be taken in this practical

  • disinfect work surfaces before and after use
  • work close to a bunsen flame
  • pass equipment through a bunsen flame to sterilise before using
• state the aseptic techniques to be taken in this practical

  to allow oxygen in to prevent the growth of harmful anaerobic bacteria
• why should the petri dish be invented during incubation

  to prevent condensation from forming on the lid and dripping down to the agar plate
• what temperature should the petri dish be at?

  a temperature which does not favour the multiplication of pathogens
• how should the area of the zone of inhibition be measured?

  place a piece of squared paper under the agar plate to measure the diameter and get the area:$\pi r^2$
• state a source of error in this practical

  the zone of inhibition may not be a uniform circle so the area may be determined accurately
• outline the procedure to prepare a plant extract

  grind the plant with a small amount of sterile water using a mortar and pestle
• outline the procedure to test the effectiveness of different anti-microbial agents

  1. on the bottom of the agar plate, divide the plate into four sections and label with the anti-microbial agent to be applied
  2. use sterile forceps to place a filter paper disc soaked in the anti-microbial agent in the center of each agar plate section
  3. tape loosely and incubate at 25 degrees celcius
  4. find the area of the clear zones
• state the controlled variables of this practical

  • size of the filter paper disc
  • concentration of anti-microbial agents
  • spread of bacteria (evenly throughout the agar plate)
• state a hazard safety precaution involved in this practical

  • bacteria is a biohazard
  • wash hands before and after the practical
  • use aseptic techniques and disinfect work surfaces