Biological indicator (BI)

A carrier, such as a paper strip, steel disc or self-contained vial, with a known population of highly resistant spores used to challenge and validate a sterilisation or decontamination process. Examples are Geobacillus stearothermophilus for steam and hydrogen peroxide, and Bacillus atrophaeus for dry heat and ethylene oxide. BIs are placed at the hardest-to-sterilise locations, and their failure to grow after the cycle shows the required lethality was achieved.