Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Sterilisation
What is Sterilisation?
The killing or removal of all microorganisms from the fermenter vessel, the growth medium and the incoming air before a culture is started. Sterilisation is carried out first, so that the vessel contains no living organisms at all; the chosen microorganism is then deliberately added in a separate step called inoculation. The two must not be confused: sterilisation removes everything, inoculation adds one thing. Sterilisation matters because unwanted microorganisms entering the fermenter would compete with the chosen organism for nutrients, reduce the yield, alter or spoil the product, and in some cases create a safety risk.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.
Common mistakes with Sterilisation
- “Sterilisation means adding antibiotics to the culture.” Why wrong Sterilisation happens before the culture starts and removes all microorganisms, including the one you are about to add. Say instead The vessel and medium are sterilised and the incoming air is filtered, and then the chosen microorganism is inoculated into the sterile vessel.
Questions students ask about Sterilisation
What is the difference between sterilisation and inoculation?
Sterilisation kills or removes all microorganisms from the vessel, the medium and the incoming air, and happens before the culture starts. Inoculation is the deliberate addition of the one chosen microorganism afterwards. Sterilisation removes everything; inoculation adds one thing.