D-Value Estimation

The quality of control tests of H₂O₂ decontamination processes strongly depends on the used microorganism. Therefore, biological indicators are always certified with an underlying strain.

Since biological indicators are to be used without a special containment facility, bacterial spores are required that retain their resistance properties over the specified shelf life. Bacterial spores of Geobacillus species are therefore usually used for biological indicators.

The quality control team of SKAN Laboratories provides appropriate test methods to control the microorganisms used for biological indicators and to document their use based on recognized standards.

In order to reliably answer the question about the quality of a decontamination based on H₂O₂, the batch of the biological indicator must be homogeneous with respect to existing resistances. For the test, the biological indicators are placed in the plant or isolator and the well-known decontamination procedure is performed as standard. The indicators are then analyzed to determine whether they are inactivated. The degree of inactivation can be derived as the quality of decontamination.

The SKAN Laboratories quality control team performs the Total Kill Test based on recognized standards with high quality documentation using a reference SKAN H₂O₂ decontamination system.

The decimal reduction time describes the amount of time required to kill 90 % of a specific microorganism. This time period is referred to as the D-Value. The determination of this D-Value is a mandatory requirement for the quality control of batches of biological indicators. The D-Value determination determines the informative value of the biological indicators, which are subsequently used to verify the H₂O₂-based decontamination.

The SKAN Laboratories team is experienced in the determination of the D-Value and performs all control procedures based on recognized standards.

In order to be able to determine the quality of decontamination tests, SKAN has developed a method for counting viable, isolated spores. The method is based on the scientific principle that spores are capable of germination and growth on solid culture media, and that each microbial colony-forming unit (CFU) represents a direct progeny of a single spore in the original inoculum.

This is done by serial dilution of the spore in a suitable medium after resuspension from the carrier. The final dilution is then plated out on a suitable medium. After the spores have grown into colonies on this medium, they are counted. The Viable Spore Count results correspond to the amount of Geobacillus stearothermophilus spores that were initially inoculated on the biological indicator.