Quality control of microbial characterisation tests, culture media and antimicrobial susceptibility determinations is best accomplished using microorganisms with well-documented and stable phenotypic and genotypic characteristics.
Bacterial and fungal strains have been selected and recommended by expert bodies, such as the International Organisation for Standardisation (ISO), EUCAST, CLSI and the European Pharmacopoeia, on the basis of their suitability for monitoring test performance and ensuring the validity of results for testing used in clinical, food, pharmaceutical, water and veterinary laboratories. Products derived from the cultures in the collections should be manufactured using the minimum number of sub-cultures, to minimise the possibility of alterations to the phenotype due to mutations. Selectrol strains are manufactured exclusively from Public Health England Culture Collections (NCTC® and NCPF®) and are first generation subcultures. They are preserved during long-term storage as freeze-dried cells in order to minimise any alterations to the phenotype caused by mutations.
A Selectrol® disc provides a first generation subculture that originates from a master culture sourced from Public Health England Culture Collections. The growth from the Selectrol® disc provides a working stock for laboratory testing. It is generally accepted that no more than a total of five passages should be made from the master culture, in order to avoid genetic drift and mutant selection. Therefore, no more than four passages (fresh cultures) from the working stock should be made.
For most strains, Selectrol® discs are guaranteed to contain at least 106 organisms at the time of purchase; this number is sufficient to ensure that when the discs are used and stored as directed there will be viable organisms cultivable until the stated end of the shelf life, which is usually 9 months from the time the vial is first opened.
Selectrol® batches are tested in our UKAS accredited testing laboratory number 2496.