Review Notes DETAILS


 Biological indicator (BI): “Test system containing viable microorganisms providing a defined resistance to a specified sterilization process.”
Process challenge device (PCD): “Item designed to constitute a defined resistance to a sterilization process and used to assess performance of the process.”
A biological indicator is the most accurate method of monitoring sterilization effectiveness.
Biological Indicator (BI) monitoring is also called Spore Testing,
Biological indicators are intended to demonstrate whether the conditions in the sterilizer were adequate to kill a large number of highly resistant bacterial spores or organisms
Biological monitoring provides the only direct measure of the lethality “killability” of a sterilization cycle
Ampoules or vials containing a paper strip injected with Bacillus stearothermophilus spores in a growth promoting solution are used for BI testing in steam sterilization.
Bacillus stearothermophilus spores are used because they demonstrate a high resistance towards steam.
A BI is placed in the sterilization chamber together with the load. The sterilization process is then run to completion.

At the end of the sterilization cycle how do you determine that the spores were all killed?
The BI is placed in an incubator which is designed to promote growth for live spores. The period of incubation is stated in the manufacturer’s IFU.
If all the spores were killed during the sterilization, there should be no growth or no color change in the ampoule in the incubator.
The test is considered NEGATIVE test or a PASS if there’s no color change or signs of live microorganisms
However, if there’s any color change, normally a yellow color in the ampule, it implies that not all the spores were killed during the sterilization cycle or there are still some live bacteria in the ampule. This is a POSITIVE TEST or a FAIL. If the test is positive, the items in the load cannot be used. They will have to be recalled and processed again

How do you rule out the possibility that the ampule that was included in the sterilization contained dead spores or microorganisms before they were placed in the sterilizer?
This is determined by using another ‘fresh’ unused ampule from the same lot as the one used for the test. This ampule which has not been sterilized, and supposed to contain LIVE spores is placed in the incubator with the BI that was just removed from the sterilizer. The two are monitored for growth in the incubator. The live bacteria in the test ampule, which is called the CONTROL is expected to grow and the color within the ampule is expected to change or become cloudy. That is a POSITIVE test is expected with the CONTROL BI. However, if there is no color change or growth in the control ampule then most likely the spores in the ampules from the lot were already dead and therefore the ampules from that lot are not good for testing. In that case the test result cannot be validated, the incident should be reported and investigated. The incubator function should be checked as well.
It is recommended to run the CONTROL, at least each day a BI is run. Also, a control should be run anytime a new lot is opened.
While a positive result is expected from a CONTROL test, a negative result is expected for a BI test that has completed a sterilizer cycle. Any result outside this expectation is a cause for investigation.

* * The control should be picked from the same manufacturing date and lot number as the processed biological indicator

The PCD containing the BI should be placed flat in the most challenging location in the chamber.
Typically, PCD is placed on the bottom shelf near the drain for steam sterilization

If the test BI failed, (POSITIVE RESULT) the use of the sterilizer must be discontinued and the result reported to the supervisor.
Any suspected non-sterile items must be recalled and sterilized again
Reasons for a POSITIVE BI result (a fail test) include operator error and sterilizer malfunction.

Operator errors may include:

  • Not placing the BI at the correct location in the sterilizer load
  • Using BI not intended for the method of sterilization being used. (each sterilization method has a specific BI designed for it)
  • Not adhering to the manufacturers instruction for use (IFU)
  • Not using the correct temperatures and pressure or selecting the wrong cycle
  • Placing the BI in the sterilizer on its side instead of laying it flat
  • Overloading the sterilizer or stacking the loads on top of each other
  • Storing Bis in adverse environmental conditions like poor temperature and humidity
    • AAMI guidelines recommend placing the BI inside a “Test Pack” to properly challenge the sterilization cycle. The test pack is referred to as Process Challenge Device (PCD).
    • AAMI recommends that every load containing an implant should be monitored with a PCD containing both a biological indicator (BI) and a Class 5 integrating indicator (CI)
    • Both AAMI and AORN strongly recommend that load containing implant should NOT be released, but quarantined until results of the BI are known.

Results are known after incubation.

  • If a surgeon insists on having an implant be released before the BI results are known due to an emergency, the release must be documented providing a reason for the release.
  • AAMI suggests doing routine sterilizer efficacy monitoring preferably daily, with a full load, using a PCD containing a BI.

The possibility of a recall is the reason why so many Healthcare facilities perform daily or even every load biological testing


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