Biological Indicators (BIs): What Are They and How Do They Work
Written by: Domhnall Mc Gowan M.Sc.
What is a BI?
A biological indicator is broadly defined as a characterized preparation of a specific microorganism that provides a defined and stable resistance to a specific sterilization process. Microorganisms widely recognized as suitable for biological indicators are spore-forming bacteria because these microorganisms are significantly more resistant than normal microflora.
Biological indicators are used in processes that render a product sterile in its final package or container, as well as for the sterilization of equipment, materials, and packaging components used in aseptic processing. Biological indicators are also used to qualify sterilization cycles and are used in periodic revalidation of sterilization cycles.
Biological indicators can come in a few forms such as discs, paper strips, metal strips and glass slides. BIs are always packaged in a way which protects them from contamination while being stored and transported and before use.
Geobacillus Stearothermophilus (G. stearothermophilus)
The type of microorganisms chosen to be used as BIs are ones which tend to be difficult to eliminate/inactivate. Succinctly, if your sterilization cycle can inactivate a BI then it can likely eliminate normal environmental microorganisms.
G. stearothermophilus (previously known as Bacillus stearothermophilus) is a common bacteria used in BIs. Its use in BI strips stems from its inherent environmental resistance properties. It is a spore forming bacteria and a thermophile meaning it is resistant to heat and difficult to eradicate using normal everyday sterilization methods. Additionally, G. stearothermophilus is nonpathogenic so it is relatively safe to handle.
Due to its robust environmental resistance G. stearothermophilus is an ideal microorganism to challenge your biodecontamination or sterilization process. BIs inoculated with G. stearothermophilus usually come as strips (paper or metal) or discs which have a defined number of spores on them, depending on what sterilization assurance level (SAL) you need to achieve from your cycle, this number can vary.
To use BIs, you must place them in the space, or on the material, that you are decontaminating and then run your cycle. During the cycle your sterilant (hydrogen peroxide, heat, ethylene oxide etc.) contacts the BI and begins to kill the spores. Following the completion of the cycle the BIs are collected, placed in culture media, and incubated. If the cycle was designed correctly and successful, then there will be no growth observed following incubation.
Validating Your Decontamination Process
Validation of your decontamination or sterilization process is extremely important to perform before relying on it for any operational needs and is a requirement in many regulated industries. Validation includes the decontamination cycle design, cycle qualification, and continued cycle reverification.
BIs are an excellent tool, and in some cases the prescribed tool, for qualifying your decontamination cycle.
When planning your cycle validation process it is good to be cognizant of the expertise and additional requirements that are needed, which you may not have on hand. You need:
- Experienced cycle development personnel
- Validation personnel
- Microbiology labs with specialized incubators
- BIs and BI culture media
- Personnel to read and record results
Cycle validation is a time and labor-intensive process to perform correctly, and unless you have an established validation team and microbiology lab then investing in in-house cycle validation is not cost effective. It is more efficient to work with a 3rd party who can guide you through the process, help design your cycle, execute the qualification, provide the materials, and handle the results.
Vibraclean are experts in cycle development and qualification using ionized hydrogen peroxide (iHP). Vibraclean have worked with many pharmaceutical and biopharmaceutical companies in North America, helping them with validating their sterilization cycles. From cycle development and design, to executing the qualification process, and handling the incubation and results Vibraclean can offer a turn key solution for validating your sterilization cycle.