The validation requires a microbial sample that is highly resistant to a particular method of sterilization.
Hence there are different sets of microbes prescribed for different methods of sterilization.
Steam sterilization validation: A strip containing spores of geobacillus thermophilus is placed in different corners of the autoclave chambers before the start of sterilization. Once the process is done, these probes are taken out and cultured in media.
Dry heat sterilization using a hot air oven is validated by using spores of bacillus subtilis species.
Gaseous sterilization using ethylene oxide Bacillus subtilis var niger is used.
Radiation sterilization: The validation is done by using spores of Bacillus pumilus. But this process is not necessary as a lethal dose of radiation is followed without any doubts for effectiveness.
For filtration sterilization, Serratia marcescens is used to check the efficiency of filtration sterilization.
It is done using suitable biological indicators.
The probe of biological indicators is kept along with the sample for the complete period of sterilization.
The probes mostly have microbes like bacteria.
Once the sterilization process is completed, the probes are kept in nutrition media to check the survival of microbes in it.
Effective sterilization destroys all the bacterial spores during the process.