Free Culturing Microorganisms OCR A Level Biology revision notes – covering specification points 6.2.1(gi) and 6.2.1(gii).
Microorganisms can be cultured (grown) intentionally for commercial and research purposes under controlled conditions.
Microorganisms are typically cultured in a culture medium* containing the required nutrients (e.g. carbohydrates, nitrogen) that is sterilised before the inoculation (introduction) of the desired microorganisms.
*Also referred to, informally, as a growth medium.
Culturing microorganisms involves sterilisation, inoculation and incubation:
- Sterilisation kills all microorganisms present in the culture medium or on the equipment.
- Inoculation transfers the microorganisms to the culture medium.
- Incubation maintains the microorganisms at a suitable temperature so that they grow and reproduce.
Aseptic technique is used throughout the process of setting up cultures to ensure the sterility of the equipment and culture medium is maintained.
Aseptic technique refers to a set of procedures that prevent the culture from being contaminated with unwanted microorganisms.
A simple method for setting up a bacterial culture on agar using aseptic technique is outlined below:
- Disinfect the work surface, wash hands, and light a Bunsen burner near the working area.
- Sterilise the culture medium and all equipment in an autoclave at 121 °C for 15 minutes.
- Pour the molten agar into a Petri dish and allow it to set.
- Remove the lid of the bottle containing the bacteria and flame the neck of the bottle.
- Sterilise the inoculating loop in the Bunsen flame until it is red-hot, then allow it to cool.
- Dip the loop into the bacterial culture, then flame the neck of the bottle again and replace the lid.
- Lift the Petri dish lid slightly, and quickly streak the loop gently across the surface of the agar.
- Flame the inoculating loop after use to sterilise it.
- Tape the lid of the Petri dish without sealing it airtight, and label it.
- Incubate the dish upside down at a suitable temperature (e.g. 25 °C) for an appropriate time.