Biological Indicator

Biological Indicator for Autoclaves

A biological indicator (BI) is an essential component of sterilization process quality assurance, particularly for autoclaves that use steam to sterilize instruments and equipment.
Biological indicators are used to verify that the sterilization process effectively eliminates microorganisms, including bacterial spores, which are among the most resistant forms of life to sterilization methods.

Purpose

To document and confirm that sterilization cycles are capable of destroying all relevant microorganisms — including the most resistant spores — thereby ensuring that instruments and equipment are safe for use.

Composition

Spores:
Most biological indicators contain specific spore‑forming species such as Geobacillus stearothermophilus (commonly used for steam sterilization) or Bacillus atrophaeus (used for dry heat or gas sterilization).
These spores are selected because of their high resistance to sterilization conditions.

Growth Medium:
BIs also contain a nutrient medium that supports spore growth.
If sterilization fails, surviving spores will grow and produce a visible change in the medium — typically a color shift.

Use

Placement:
BIs are typically placed in the center of the load or in areas that are the most difficult to sterilize (e.g., inside lumens or tightly packed materials).

Cycle:
After the autoclave cycle is complete, the BI is removed and incubated at the recommended temperature for a specified time (usually 24–48 hours).

Evaluation:
After incubation, the BI is checked for signs of microbial growth.
A color change in the medium indicates that spores have survived, meaning the sterilization process was unsuccessful.

Interpretation of Results

• Negative Result:
  No microbial growth — sterilization was effective, and all spores were destroyed.

• Positive Result:
  Signs of growth (color change) mean the sterilization process was insufficient, requiring investigation and corrective action. 

Frequency

Biological indicators should be used regularly as part of a sterilization quality control program — often weekly, whenever new types of loads are sterilized, and after maintenance or repairs of the autoclave.

Importance

Using biological indicators in autoclave processes is vital for patient safety and infection control in healthcare settings.
They are considered the most reliable method to verify sterilization efficacy and to prevent infections caused by improperly sterilized equipment.

Conclusion

Biological indicators are a critical component of the autoclave sterilization process.
They not only help document sterilization effectiveness but also uphold patient safety and quality standards within healthcare facilities.
Regular use and proper evaluation of BIs are essential to ensure that sterilization practices comply with current guidelines and standards.