Within a hospital’s infection prevention and control (IPC) system, biological indicators (BIs) are considered the gold standard for verifying the effectiveness of sterilization processes.
Unlike other monitoring methods, BIs contain bacterial spores that are highly resistant to sterilization agents. If a sterilization cycle is capable of destroying these spores, it can be inferred that other pathogenic microorganisms have also been eliminated.
Two commonly used spore strains in biological indicators include:
• Geobacillus stearothermophilus → used for steam sterilization and hydrogen peroxide/plasma sterilization
• Bacillus atrophaeus → used for ethylene oxide (EO) sterilization
According to recommendations from WHO, CDC, and AAMI ST79, biological indicators should be used to:
✔ Routinely monitor sterilization effectiveness
✔ Test critical sterilization cycles
✔ Confirm the safety of medical devices before clinical use
Why Does Each Sterilization Method Require a Different Biological Indicator?
Each sterilization technology uses different sterilizing agents, therefore it is necessary to select microorganisms with the highest resistance to that specific agent in order to create a rigorous biological challenge for the sterilization process.
1. Monitoring Steam Sterilization
Steam sterilization is the most widely used method in Central Sterile Services Departments (CSSD) due to: High microbial killing efficacy. Stable sterilization cycles (121°C or 132–134°C). Compatibility with most surgical instruments
Biological indicators used for this method contain Geobacillus stearothermophilus spores, which are highly resistant to moist heat.
Currently, several types of BIs are available for steam sterilization with different result readout times:
- BT222 provides results in approximately 1 hour, commonly used to verify sterilization cycles performed during the day.
- BT224 provides results in approximately 20 minutes, allowing faster verification and supporting facilities that require rapid instrument turnover.
-BT225 is a near-instant BI system, providing results in about 7 seconds, enabling confirmation of sterilization effectiveness immediately after the cycle is completed.
Rapid-read BIs utilize spore enzyme detection technology. If the spores remain viable, their enzymes react with the medium to produce a fluorescent signal, allowing the system to detect results much earlier.
-> For instant BI technologies, the system can detect biological activity of spores immediately after the sterilization cycle, which is particularly valuable in urgent situations requiring rapid instrument turnaround.
2. Monitoring Hydrogen Peroxide Plasma Sterilization
Plasma sterilization uses hydrogen peroxide in a plasma state, which can destroy: Proteins, DNA, Microbial cell membranes
This method is commonly used for: Heat-sensitive medical devices, Endoscopes, Instruments with complex structures
Biological indicators for plasma sterilization also use Geobacillus stearothermophilus spores.
In practice, plasma BIs are available with different readout times:
- BT96 provides results in approximately 30 minutes, typically used for routine plasma sterilization monitoring.
- BT98 provides results in approximately 5 minutes, suitable for endoscopes and devices requiring rapid turnaround.
The use of rapid-read BIs enables CSSD departments to detect sterilization failures early without disrupting clinical operations.
3. Monitoring Ethylene Oxide (EO) Sterilization
Ethylene oxide sterilization uses EO gas, which sterilizes by alkylating proteins and DNA of microorganisms.
This method is typically used for: Plastic medical devices, Catheters, Heat-sensitive materials...
Biological indicators for EO sterilization use Bacillus atrophaeus spores, with a readout time of approximately 4 hours (BT110), which aligns with the long sterilization cycles typical of EO processes.
Why Are Rapid-Read Biological Indicators Becoming Increasingly Important?
In the past, conventional BIs required 24–48 hours to obtain results, which created several challenges:
• Instruments had to be quarantined while waiting for results
• Increased investment in additional instrument sets
• Sterilization failures could be detected too late
The introduction of rapid-read BIs and instant-result BIs has helped address these limitations.
Key benefits include:
✔ Immediate detection of sterilization failures after cycle completion
✔ Faster instrument turnaround
✔ Reduced workload pressure for CSSD
✔ Improved patient safety
➡ Biological indicators are not merely testing tools; they are a core component of a hospital’s sterilization quality assurance system. With new technologies such as instant-result BIs, CSSD departments can manage sterilization processes faster, more accurately, and more safely, allowing instruments to be released for use immediately after sterilization.
-> If you are interested in learning more or need consultation on
biological indicators compatible with your incubator/reader system, please feel free to contact
Duong Gia at
+84 93 955 6666 for further support.