Testing of Biological Indicators (BIs)

What is a biological indicator?

Biological indicators are generally strips, discs, (either metal or paper), or threads impregnated with a known microorganism at a measured resistance and population that represents the reference organism for the sterilization technology used.

What are biological indicators used for?

BIs are tested in support of sterilization validations and routine product release for ethylene oxide sterilization and steam sterilization technologies.

What are the different types of biological indicators?

There are two types of biological indicators: self-contained and those contained in a glassine envelope.

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 contained in a glassine envelope are inoculated with bacterial spores, and may be placed within a process challenge device that is meant to lend additional resistance to the indicator.

What is the biological indicator testing process?

Product, with indicators attached, is subjected to the gaseous sterilization method.

The BIs are placed during validation to assess the challenge of the product bioburden to the sterilant and establish a comparison of the resistance of the product bioburden and the BIs. Process Challenge Devices (PCDs) are often also used in this aspect of the validation. The BIs might also be placed during routine sterilization processing for product release.

Since bacterial endospores are usually challenging to sterilize, their presence/absence in the final sample is used to determine sterility assurance levels (SALs) and validate the gaseous sterilization process.

Finally, the biological indicators are removed from the product and sent to STERIS Laboratories to test for presence/absence of the BI indicator microorganism.

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

Bacillus atrophaeus spores are used for EO sterilization monitoring.

Which bacteria is used for biological monitoring for steam sterilization?

Geobacillus stearothermophilus is used for steam sterilization monitoring.

What are the industry standards for biological indicators?

General requirements for BIs can be found in ISO 11138-1, with the specific requirements for EO and steam in ISO 11138-2 and ISO 11138-3, respectively.

STERIS offers:

  • Integrated biological indicator testing with EO validation and/or routine sterilization
  • Product inoculation with BI strips for evaluating sterilization process
  • Collaboration with Customers in reduced incubation time (RIT) studies

Biological Indicator testing is used for validation and routine monitoring of:

  • Medical device sterilization
  • Pharmaceutical sterilization

Related content:

TechTip: Biological indicator population verification test

TechTip: Selection of appropriate internal process challenge devices (PCDS)

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