Biological Indicators (BIs) are critical to sterilization assurance.
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Comprehensive sterilization monitoring is more than checking cycle temperatures and times. It’s verifying that conditions within a load were adequate to kill a population of resistant microorganisms. A biological indicator (BI) is the only way to directly measure the lethality of a sterilization cycle.
BIs are made using bacterial spores that are even harder to kill than any potential remaining microorganisms that may have survived the surgical equipment decontamination process. When the sterilization cycle is sufficient to kill the spores in the BI, it can be assumed the microorganisms on the instruments are also killed.
Biological Indicators vs. Chemical Indicators
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Chemical indicators (CIs) verify that required amounts of time and levels of temperature and sterilant (whether steam, vaporized hydrogen peroxide or ethylene oxide) were reached inside the sterilizer or individual package. CIs will reach their end point (e.g., change color) to show that the load was exposed to the right temperature and/or sterilant. They are an important part of the sterilization assurance process, showing you immediately that one or more critical sterilization parameters were met. CIs do not measure lethality because there are living spores that will die as part of the process. CIs are still an important indicator to any sterilization program — they can provide immediate results to ensure they were exposed to the correct sterilization conditions.
However, CIs do not tell you if the potentially infection-causing microbes present in that load were exposed to a lethal dose of sterilant. Only a BI can do that. BIs are used to monitor the effectiveness of sterilizers and individual sterilization cycles.
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The theory behind the BI is that if your process is effective enough to kill a large population of highly resistant spores, it will also kill a lower number of less resistant organisms on the medical devices. Because it detects the killing of microbial spores, a BI is capable of yielding information that is more valuable than any other sterilization monitor. After exposure to the sterilization process, self-contained BIs are activated to provide the spores with optimized growth media, and then must be incubated at the appropriate temperature to determine if any spores survived. For this reason, results are not immediately available. However, advances in BI technologies have led to Rapid Readout BIs, which provide the end user with actionable results in less than 30 minutes.
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Understanding SAL
Sterility is defined as being free from all living organisms.1 It is not practical to test every single device processed for the absence of microorganisms, so sterility is assumed according to the statistical probability that a given process killed every microorganism.
The sterilization assurance level (SAL) is a number that tells you the probability of there being a non-sterile unit in a validated sterilization process.
The number expresses the likelihood that a microorganism survived the sterilization process — and can never be zero. For example, a SAL of 10-6 (or 10 to the negative sixth power) indicates that there is one chance in a million that a device is not sterile.
Biological indicators are used to develop and validate sterilization processes, and therefore estimate SAL.
BIs are key to complying with standards and guidelines — and protecting patient safety.
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AAMI standards specify that BIs are "the only sterilization process monitoring device that provides a direct measure of the lethality of the process."2 Releasing every load based on a BI result (Every Load Monitoring) is considered a best practice for sterile processing departments. A negative BI result from every single load processed confirms that the sterilizers are working.
CDC, AORN, and AAMI guidelines all state implants should be quarantined until a BI result is known, except in emergency situations.
3M leads the field with innovation after innovation.
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*Pending 510(k) clearanceAs a leader in the field, 3M has been developing and improving technology for sterilization assurance, specifically BIs, for decades. As an independent manufacturer of sterilization assurance products, 3M creates products that can be used to test the efficacy of a variety of sterilization systems and produce unbiased results.
Over the years, 3M has developed and improved technology to vastly reduce the amount of time it takes to get a BI readout. Faster readouts help you verify the safety of loads more quickly and practice Every Load Monitoring. We help you serve ORs more quickly and efficiently and ultimately, help protect patient safety.
Related Articles and Resources
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The Importance of Proper Resistance
BIs contain a known number of live microorganisms (spores) to assess the adequacy of a sterilization cycle. Because BIs measure the lethality and effectiveness of sterilizers, it's important that the spores within a BI are of the right resistance.
Sign up to download our BI comparison white paper for VH2O2.Guidelines Summary
The AAMI ST79 Comprehensive guide to steam sterilization and sterility assurance in health care facilities is a go-to resource for all healthcare facilities that process medical instruments with steam sterilization.
Get access to a convenient 3M summary of the quality assurance recommendations in the guideline.
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1. Block, Seymour S. (editor) Disinfection, Sterilization, and Preservation. 5th Edition. 2001
2. ANSI/AAMI ST79:2017 Comprehensive guide to steam sterilization and sterility assurance in health care facilities
