This is a quick introduction to sterilisation. We will go through this sterilisation in more detail in its own post, but since it is quite complicated this will just be a brief explanation so you understand the concept.
What is sterilisation?
Sterilisation is the removal or prevention of contamination at any point throughout the process.
Why do we need sterilisation?
Contamination is a big no-no in the industry. If your cell culture is contaminated, you must discard it. This is because contaminants can cause danger to the end user of the product. If your product is contaminated with bacteria and someone ingests/ injects it, they could get seriously sick. Therefore regulatory bodies require that there is no contamination present at any point of the process. Also, contaminants can compete with your cell line for nutrients and oxygen in the broth, which will reduce cell numbers, and could stop production of your product.
Levels of sterilisation required
- No sterilisation: Process does not need to be sterile. This is mainly for processes that do not create a product that will be ingested i.e. Waste water treatment.
- Protected fermentation: For processes that require some degree of sterility but do not tend to get contaminated if treated properly i.e. disinfection of needles, pasteurisation of milk.
- Unprotected fermentation: Require a high degree of sterility due to high likelihood of contamination if exposed to the external environment. This goes for bioprocesses that grow cells in media since media contains many components (nutrients, oxygen, etc.) that are highly favourable by contaminants i.e. bacteria.
Examples of contaminants
- Bacteria
- Viruses
- Mycoplasm
- Fungi
How do you avoid contamination?
Bioreactors usually operate as closed systems, meaning they do not exchange any material with the environment around it. Here are some methods of preventing contamination in reactors:
- Sterilise the reactor and any ancillary equipment (parts that you attach to the reactor)
- Sterilise whatever is going into the reactor (air, buffers, media, nutrients, etc.)
- Introduce a pure inoculate (cell culture) and feed. Before introducing the cells into the reactor make sure they are not contaminated (using a viable cell count to detect unusual growth). The feed should also be sterilised before introducing it to the reactor.
- Maintain an aseptic operation. Make sure the bioreactor is properly sealed and there are no cracks or holes that expose it to the external environment.
Methods of sterilisation
Inactivation/ killing of viable microbes
This can be done by:
- Heat treatment (heating the components to a high temperature to kill contaminants)
- Irradiation
- Chemical treatment (using strong chemicals i.e. disinfectants to kill contaminants)
Physical Removal of microbes
- This can be done using filtration or centrifugation.
If you have any questions, please leave a comment below and I will get back to you ASAP!
Bioprocessing Explained 