Aseptic Techniques (WJEC GCSE Biology)

Aseptic Techniques

• The study of microorganism growth may involve the following:

  • Inoculation

    • Inoculation is the purposeful transfer of bacteria into a sterile growth medium

    • E.g. nutrient agar in a Petri dish can inoculated with bacteria or fungi

  • Plating

    • Inoculation of nutrient agar in a petri dish is known as plating

      • E.g. bacteria samples are spread out over the surface of an agar plate using an inoculating loop

      • This separates microorganisms and allows individual bacteria colonies to be observed

  • Incubation

    • Following plating the inoculated agar plates can be incubated at a set temperature for a specified time period

    • Schools and laboratories will have different rules and regulations as to the temperatures that can be used for incubation

• During all of the processes described above it is essential that aseptic techniques are used; this prevents:

  • Release of infectious microorganisms into the environment

  • Contamination of cultures with unwanted microorganisms

Examples of aseptic technique

• Sterilise Petri dishes

  • This involves heating equipment to a high temperature to kill microorganisms 

• Sterilise nutrient agar

  • This should be carried out before the agar is poured into the sterile Petri dishes

• Disinfect work surfaces with disinfectant or alcohol before inoculation

• Work next to a lit Bunsen burner

  • This creates convection currents that stop contaminants from falling onto the growth media

• Use flamed inoculating loops or sterile swabs when transferring cultures 

  • Heating loops until red-hot kills any unwanted microorganisms

  • This should be done both before and after inoculation

• Keep the lid on Petri dishes when not in use, and lift the lid at an angle during inoculation

  • This reduced contamination risk from airborne microorganisms

• Tape the Petri dish lids closed after plating

  • Loss of Petri dish lids could lead to the escape of potentially harmful microorganisms

• Incubate plates at a safe temperature of 25 °C

  • This prevents the growth of pathogenic microorganisms which are more likely to grow at human body temperature

• Sterilise or dispose of all equipment after use

Inoculation diagram

Aseptic techniques ensure safety while carrying out inoculation of nutrient agar