Biological Indicator Testing

Testing of Biological Indicators (BIs)

What is a biological indicator?

Biological indicators (BIs) are test systems that have microorganisms of known high resistance deposited onto a substrate, generally in the form of strips, discs, (either metal or paper), or threads with a defined resistance and population for the sterilization technology used.

What are biological indicators used for?

Biological indicators manufactured in accordance with ISO 11138-1 are used and tested in support of sterilization validations and routine product release primarily for gaseous sterilization technologies for medical devices and pharmaceuticals.

BIs are utilized during validation activities to provide a microbiological challenge of known high resistance to a sterilization process. Through comparative resistance studies, BIs are demonstrated to be an equivalent or typically greater challenge than the natural bioburden on the product. In validation, the BI is then used to demonstrate the attainment of a minimum sterility assurance level. Process Challenge Devices (PCDs) are often also used
in this aspect of the validation. If parametric release is not validated, BIs are also used during routine sterilization processing for product release.

Bacterial endospores are used as challenge microorganisms, due to their resistance characteristics, which is quantified during manufacture in a Biological Indicator Evaluation Resistometer.

What are the different types of biological indicators?

There are multiple types of biological indicators, the most prevalently used being spore strips requiring 7-day incubation for results and self-contained BIs with reduced incubation times, less than 7 days. Self-contained biological indicators contain the growth media in an ampoule within the same vial as the paper strip or disc. The vial is activated by cracking the media ampoule.

Biological indicator strips are inoculated with bacterial spores and may be packaged in a glassine envelope. Spore strips may also be placed within process challenge devices (PCDs) that are intended to increase the resistance to the biological indicator. PCDs increase the resistance by restricting access of the sterilant to the biological indicator by
physical barriers or tortuous pathways. Exercise caution when creating process challenge devices to ensure PCD’s are manufactured and used in manner that produces consistent resistance characteristics.

What is the biological indicator testing process?

During sterilization, a minimum quantity of BIs is distributed throughout the load. Following processing, the BIs are removed from the product and sent to STERIS laboratory testing locations to test for the presence/absence of the indicator microorganism.

Which bacteria is used for biological monitoring for ethylene oxide sterilization?

The bacteria used for biological monitoring for ethylene oxide sterilization is Bacillus atrophaeus spores.

Which bacteria is used for biological monitoring for steam sterilization?

The bacteria used for biological monitoring for steam sterilization is Geobacillus stearothermophilus.

What are the industry standards for biological indicators?

The industry standards for biological indicators and general requirements for BIs are found in ISO 11138-1, with the specific requirements for EO and steam in ISO 11138-2 and ISO 11138-3, respectively.

Why should BIs be enumerated at point of use?

BIs will have storage conditions stipulated by the manufacturer. Upon BI receipt, user should enumerate a sample of the BIs as confirmation that the BIs still meet the acceptance criteria for population verification, which is -50%/+300% for Bacillus atrophaeus in accordance with ISO 11138-2

STERIS offers:

Population verification of purchased BIs
Biological indicator testing with EO validation and/or routine sterilization
Product inoculation with BI strips for validation activities
Collaboration with Customers in reduced incubation time (RIT) studies

Microbiology Supplies

STERIS offers many types of BIs and PCDs available for purchase, provided with population verification test results executed in accordance with ISO 11138. Our stock items are immediately available with no minimum order quantity. Orders from stock inventory typically ship within 2-3 business days. Special orders may also be available for non-inventory supplies (minimum order quantities and lead times may vary).

Go here for a complete list of our microbiology supplies. To place an order, email a completed, signed supply purchase request form to BROLab@steris.com.

Contact us to find out more about our global contract sterilization, testing, and validation services.