Lyophilisation: Long-term storage for bacterial strains
Lyophilisation, also known as freeze-drying, is a preservation method achieved through dehydration. The process was developed initially in 1906 and the technique currently applied by NCTC is an adaptation of the method used during World War II to preserve and transport blood serum.
The majority of bacterial strains in NCTC are supplied as lyophilised cultures in glass ampoules which have been flame-sealed under vacuum. This format is particularly suitable for long term preservation of organisms.
By using this method, strains of the Enterobacteriaceae family will remain viable for more than 50 years and most anaerobic organisms will survive for approximately 20 years. The very earliest strains from NCTC’s valuable collection date back to 1915 and continuous use of this technique has been paramount in preventing excessive manipulation of strains over the years, ensuring bacterial passage between batches is kept to a minimum and reducing laboratory adaptation of the organisms available through the NCTC catalogue.
The freeze-drying process occurs in several steps. Initially organisms are cultured using good aseptic technique, preferably on non-selective media without the addition of antibiotics. Once grown, a cell suspension is made in a cryopreservation medium/buffer. The samples are then subjected to the freeze-drying process involving freezing at a temperature below -40°C and then controlled drying under vacuum. The freeze-dried strains are stored at between 4°C and 10°C and are tested regularly for viability.
Contract freeze-drying
In response to numerous requests, NCTC has re-introduced a freeze-drying (lyophilisation) service for those who wish to have their own bacterial or fungal cultures preserved, thereby ensuring the properties of their strains are maintained during long term storage periods.
In order to do this the requestor will need to supply an identifying number with a maximum of 12 characters for their batch, and it is also advisable to agree in advance not only the number of ampoules/vials required but also the information to be included on the label. This will reduce the preparation time needed before the cultures are submitted to be freeze-dried.
A lyophilisation, viability and purity report to ensure full traceability of the entire process is provided with the end product. Additional bacterial characterisation can also be performed upon request.
Cultures can be preserved using this method in one of two formats:
Glass Ampoules - In addition to all the benefits stated above, this effective long term preservation also removes the need for -80°C cryogenic beads storage and is recommended for individual researcher and commercial collections. We can accept Hazard Group 3 organisms for this technique. Ampoules can be produced in multiples of 10 up to a maximum of 180.
Capped Vials - This service consists of preparing freeze-dried cultures in vials with a rubber closure held in place by a crimped foil, easy-opening cap. Although these vials are easier to open and manipulate than the glass ampoules, a shorter shelf life of two years is recommend for cultures preserved using this method. This format is therefore highly appropriate for specimens produced for external quality assessment (EQA) scheme distributions, where large numbers need to be produced for dispatch to multiple scheme participants and also for routine internal quality control (IQC), where extended storage is not the key priority. Vials can be produced in multiples of 100 up to a maximum of 500.
NCTC has over 50 years experience of freeze-drying bacterial strains and has collated a large viability data set which supports the suitability of freeze-drying for prolonged storage. If you are interested in finding out more about this service please contact us with your requirements. culturecollections@phe.gov.uk
Links
NCTC contract freeze-drying services