Biological indicators (BI) provide the best assurance of sterility by challenging the sterilizer with quantifiable, highly resistant spores. Biological indicators are used for load control monitoring which is theprocess by which a load is monitored and released based on the result of a biological indicator in a test pack.
The self-contained BI for 121°C (250°F) gravity air displacement steam cycles consist of a Bacillus stearothermophilus spore strip; sealed glass ampule with growth medium and a bromocresol purple pH indicator system; brown color-coded cap with holes for sterilant penetration and a hydrophobic filter as a bacterial barrier, and a chemical indicator on the label that changes from rose to brown when processed. After sterilization, the vial is "crushed" to add the growth media to the processed spore strip. The BI is incubated for 48 hours for a visual change readout. A color change to yellow indicates surviving spores and a positive result.