GKE Australia Biological Indicators
Sterilization procedures in hospitals have reached a high standard of quality. Necessary monitoring procedures are costly, however important, to ensure long-term asepsis in all fields of surgical operations.
International and local standards and directives. e.g. the European Medical Device Directive (MDD) re-quire validation, batch monitoring and documentation of sterilization processes.
Besides industry, healthcare facilities must follow the same validation, monitoring and documentation procedures. Validation and monitoring of sterilization processes is carried out by parametric, chemical and/or biological tests. The validation using biological indicators is necessary if:
- the structure of the goods to be sterilized is such that physical sensors cannot be applied (e.g.: small holes, gaps, sealed areas, coatings with oils etc.)
- lumens of hollow devices are so tiny that the temperature difference between non-condensable gas-es (inside) and steam (outside) is not detectable. Gases in such small lumens of several 100 μl heat up very quickly to the steam-temperature-level.
- the presence of water condensate cannot be detected by physical means (e.g.: If the temperature gradient in the process is so slow that encapsulated non-condensable gases have time to heat up and do not show a detectable temperature difference.)
- the surface structure of the medical devices requires specific testing (e.g.: porous rubber stoppers)
- the sterilizing agent, the goods to be sterilized and/ or packaging contain salts. The salts may get dissolved in the condensate film and cause big changes of the resistance characteristics.
- the condensate contains substances changing the pH-value (e.g.: corrosion-inhibitors) or the material of medical instruments (e.g.: aluminium surfaces) may react with water creating basic hydroxides.
In above cases all surfaces or liquids have to be inoculated with biological indicator suspensions. After a validated population determination, reduced process cycles have to be carried out to achieve survivor curves to determine the kill kinetics on/ in those critical areas. For porous loads and hollow process chal-lenge devices (PCDs) biological indicators may be used to monitor the process conditions in such critical internal areas.
Biological indicators are defined in the European and International Standards EN ISO 11138 parts 1-5. For most of the commonly used sterilization processes special reference biological germs have been selected, such as Geobacillus stearothermophilus for steam, formaldehyde and hydrogen peroxide sterilisation processes, Bacillus atrophaeus for ethylene oxide and dry heat sterilisation processes and Bacillus pumilus for radiation sterilisation processes.
Depending on the type of sterilization process, a special resistance characteristic of biological indicators is required, to prove the success of a defined sterilization process. During such a sterilization process the spore population always decreases due to the exponential kill characteristic called reaction kinetics first order. The population however, will never reach an absolute 0-value. Therefore modern definitions of goods declared “sterile” do not specify the absolute absence of biological activity, but determine aseptic conditions with the certain probability, called Sterility Assurance Level (SAL).
According to the European Standard EN 556 the minimum SAL has to be 10-6 CFU/per part or better. This means that out of 1 million units, no more than 1 unit may show growth.
Both the kill kinetics and the penetration characteristics of a sterilization process have to be monitored. The kill kinetics is monitored by the right type of bacteria with the total resistance of a biological indicator.
The total resistance of a biological indicator depends on the population and resistance of each individual germ. The resistance of each individual germ is defined by the decimal reduction value which is the time needed to reduce the population of a biological indicator to one tenth of the original population. The total resistance of a biological indicator is expressed by the FBIO value:
FBIO = D121°C value x log (population)
This fact may be demonstrated by the 2 examples below in the table.
As seen above, the D-value of a given strain is never constant and depends on growth and process condition. Therefore, for each batch of biological indicators certificates must be associated to the product indicating the population, individual resistance and the total resistance of a biological indicator.
gke offers its Steri-Record biological indicators according to EN ISO 11138 series. All packs contain a certificate with all necessary information mentioned above.
After the biological indicator has passed the sterilization process, all treated spore strips have to remain in the glassine envelopes. They should be sent with one marked untreated spore strip to a microbiological lab. All strips should be aseptically transferred into Tryptic Soja broth (TSB) and developed for at least 7 days. If there is any doubt about the spore type, 1 ml of solution may be developed on TS agar plates (TSA) to determine the spore type. TSA vials without a spore strip should not show any growth, the un-treated spore strip should show vital growth. Growth of treated spore strips have to be determined individually (see our technical information). gke offers growth medium test tubes with pH-indicator for faster evaluation.
Self-contained biological indicators contain growth media in a separate vial and may be developed directly at the user’s site. They must not be used in dry heat processes. For information in more detail, please see our data sheet “self-contained biological indicators”.
The penetration characteristics are monitored using Process Challenge Devices (PCDs) representing the “worst-case” penetration characteristics of a load. PCDs as described in EN 867-5 “Hollow Load Test” and in DIN 58921 may be used. Biological indicators are used inside to check the penetration of the sterilization agent.
gke biological indicators are available with different D-values. If a particular D-value is required, that differes from the BI available in stock, it is advisable to check if the BI can be produced with the particular characteristics.