GCSE Biology (AQA)

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Aseptic Techniques

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Cell Biology Cell Structure

Aseptic Techniques

5:48 Culturing Microorganisms
Spec 4.1.1.6
Previous Culturing Microorganisms Next Calculating Areas of Colonies
  • Aseptic techniques are used to prevent contamination in pure cultures of microorganisms.
  • Microorganisms include small organisms like bacteria, and a pure culture contains only one type of microorganism.
  • Contaminated cultures, where multiple microorganisms grow, can confuse experiments.
  • Pure cultures are essential for accurately testing the effects of disinfectants and antibiotics.
  • To prepare an uncontaminated culture, Petri dishes and culture media must be sterilized, often using an autoclave which heats and pressurizes equipment to kill bacteria.
  • Inoculating loops used to transfer microorganisms must be sterilized by passing through a flame to kill bacteria before use.
  • When opening vials containing bacteria samples, lids should be slightly removed to prevent air contaminants.
  • The inoculating loop is cooled after flaming before dipping into the sample to avoid killing the bacteria in the sample.
  • Bacteria are transferred to growth media, like agar in a Petri dish, using a sterile inoculating loop to streak the bacteria.
  • The inoculating loop is flamed between streaks to prevent cross-contamination and to dilute the bacteria concentration across the Petri dish.
  • After streaking, the Petri dish is sealed with adhesive tape in specific spots to prevent opening and contamination but allowing air for bacterial growth.
  • Petri dishes should be labeled with the culture type and stored upside down to prevent contamination from condensation.
  • Cultures are typically incubated at 25 degrees Celsius in school labs to reduce the risk of growing harmful microbes, while hospital labs may use higher temperatures for rapid pathogen identification.
  • After incubation, bacterial colonies will appear, showing growth patterns based on the streaking method, allowing observation of isolated colonies.

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