Biological indicators

What are Biological Indicators?

Biological Indicators are preparations of known bacteria with a stable, defined resistance thresholds and a predictable response to various sterilisation processes.  In the lab or aseptic cleanroom environment, Biological Indicators are used to periodically revalidate sterilisation protocol and confirm inactivation of pathogens.

There are at least three different types of Biological Indicators used in sterilisation monitoring, with each type using bacterial spores of known sterilisation and sterilisation procedure resistance.  It is also possible for a Biological Indicator to incorporate two distinct species of microorganisms.


Biological Indicators – Carriers

A carrier is a vessel (plastic, glass, filter paper, etc) which contains spores and is sealed so as to preserve the viability of the microorganisms. The carriers are well made and designed not to be degraded by the sterilisation process the Biological Indicator is meant to monitor, as it would compromise Biological Indicator performance. The packaging itself also undergoes aseptic manufacturing procedures to ensure it does not contain any contaminants which would affect the stability or the performance of the Biological Indicator.


Biological Indicators – Spore Suspension

Biological Indicators can also come in a spore suspension, which is then directly applied to the product, packaging, or surface that will undergo the sterilisation procedure.  Simulations of inoculated products are sometimes used in sterility monitoring, but it is usually a requirement to show the final product, which will receive the inoculation, does not alter the effectiveness of the Biological Indicator, thereby invalidation results.


Biological Indicators – Self-Contained Indicators

Self-contained indicators have packaging which contains the recovery growth medium for the microorganisms’ incubation period following sterilisation exposure.  Self-contained Biological Indicators containing both the bacteria spores and the growth medium are an enclosed system, which provides sterilisation resistance.

Sterilisation resistance of the self-contained indicator’s system depends on the length of time it takes for the sterilant to penetrate the package.  Ease of penetration is controlled through composition and design at the manufacturing level.  These types of indicators often contain a dye to indicate negative or positive growth in bacteria spores following incubation, and the sample is ready for incubation directly following the sterilisation process.


Biological Indicators versus Enzyme Indicators

Though Biological Indicators have long held the market in sterilisation monitoring, Enzyme Indicators are set to replace them as a faster, cheaper alternative.  A variety of different industries depend on Biological Indicators to provide sterilisation monitoring, and stopping research or production while waiting on Biological Indicator results to come back and be frustrating, not to mention costly.  Enzyme Indicators are able to provide instant, quantifiable results, which means no longer having to stop cleanroom or aseptic environment operations waiting for spores to incubate.

Enzyme Indicators use the thermostable enzyme Adenylate Kinase (isolated from thermophilic bacteria) as it has predictable sterilisation resistance and a quantifiable inactivation profile.  Enzyme Indicators emit light that can then be measured with a lumeometer, giving measurable data as compared to the positive or negative results received with Biological Indicators.  And unlike Biological Indicators, the results with Enzyme Indicators are immediate.   Protak Scientific is currently testing the commercial viability of Enzyme Indicators, and is striving towards bringing this fast, reliable, and accurate technology to the scientific community.