Culture Collections

Frequently Asked Questions: Bacteria


 NCTC 2021


What is a type culture?

A type culture, or type strain, is the strain on which the description of a species is based. For example, NCTC 10332 is the type strain of the species Pseudomonas aeruginosa. Although the type strain is often (but not always) the first strain of a species to be isolated and described as a new species, it is not necessarily the most typical example of that species. An example of this would be the type strain of the species Listeria monocytogenes NCTC 10357, non-motile variant of what is described as a motile species.

When describing new species, the International Committee on Systematics of Prokaryotes stipulates (as outlined in the International Code of Nomenclature of Prokaryotes) that the type strain of a species must be deposited in “at least two accessible culture collection”, such as NCTC. For more information on depositing strains with NCTC, go to: How to deposit strains with NCTC.


What is the passage number of my NCTC strain? 

NCTC microbial strains produced and distributed in ampoules by Public Health England are categorised as Primary Reference Standards and therefore considered “passage zero”, where a passage count is defined as the “transfer of organisms from a viable culture to fresh medium with growth of the microorganisms” at the recipient laboratory. Please note that NCTC cultures are not considered passage zero for the purposes of an import permit.

Additionally maintenance of bacteria in a freeze dried state reduces the need for subculture when creating new batches, and the NCTC QC regime includes testing to ensure that the cultures remain unchanged by passage in house.


Who uses NCTC cultures?

Many thousands of laboratories all over the world use NCTC cultures. The strains are used in a very wide range of fields including clinical, veterinary, food, water and environmental microbiology. They are used by public and governmental organisations, hospitals, universities and research establishments, private companies and global industries.


How can I use NCTC strains in diagnostic testing?

NCTC cultures are often stipulated as controls for specific procedures such as the strains recommended by EUCAST* for antimicrobial susceptibility testing.  They are used as positive and negative controls for phenotypic tests and can be used for evaluating and harmonising routine and specialist microbiological tests.


How are researchers using NCTC strains?

NCTC strains can be used for evaluating the efficacy of potential new drugs and alternative therapies. They are of value in studies to characterise bacterial strains, determining the prevalence of antimicrobial resistance and understanding the mechanisms associated with resistance. NCTC strains are used frequently for evaluating new methods and technologies and for assessing improvements to established methods such as PCR.


What do the NCTC cultures look like?

The NCTC cultures are provided as freeze-dried (lyophilised) micro-organisms in evacuated glass ampoules. For guidance on opening the ampoules, go to: How to open and grow freeze-dried NCTC strains


How are NCTC cultures dispatched?

Cultures are sent by courier and you would normally receive your cultures within two to five days. Cultures are dispatched as Infectious Substances, Category A (UN 2900 and UN 2814) or Infectious Substances Category B (UN3373), as appropriate. Export restrictions apply for the supply of hazardous pathogens and compliance will impact on the length of the delivery period.


What is the difference between NCTC and ATCC cultures?

There are over 500 culture collections around the world containing micro-organisms of significance in a wide range of fields. ATCC (American Type Culture Collection) is a general collection based in the US.  NCTC focuses on bacterial strains of biomedical or veterinary importance and there is some overlap between strains available from ATCC and NCTC although many NCTC strains are exclusive to our collection. For guidance on the ATCC strains that are easily available from NCTC go to: NCTC equivalents to ATCC bacterial strains


Are NCTC cultures reference materials?

Yes. You do not need to provide any validation data for the identity of strains that you have purchased from NCTC.


Still have a question? Submit a technical enquiry to our team.


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