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Putting the T in NCTC : Type strains of recently described bacterial species from clinical sources

When a new bacterial species is originally described, the description is reviewed and published in the International Journal of Systematic and Evolutionary Microbiology (IJSEM) which serves as a record of all recognised bacterial species. As a part of this process, the first isolate (strain) of the new species must be deposited within two internationally recognised Culture Collections1. It is designated the ‘type strain’, i.e. the strain on which the description of the species is based. The strain is assigned a reference number by the relevant collections (such as the NCTC number) and those reference numbers must be cited in the IJSEM paper that formally describes the species.  The new type strains deposited in each culture collection are equivalent, and type strains deposited in the two (or more) culture collections retain their status as type strains.

Depositing bacterial strains with NCTC is a free service provided by Public Health England’s Culture Collections, who also provide certificates of deposit. As both an internationally recognised culture collection and a collection with a focus on bacteria of medical and veterinary relevance, NCTC is ideally placed to support the discovery of new medically relevant species, with expertise in the cultivation, preservation and knowledge of the scientific considerations for describing new bacterial species.

Although not an exhaustive list, below are some of the type strains of recently described bacterial species from clinical sources, now available for reference from NCTC.

NCTC 13537THaemophilus sputorum (Nørskov-Lauritsen et al. 2012)2

Haemolytic species from the genus Haemophilus are frequently isolated from the nasopharynx or throat and can either exist in the human body as commensal organisms (part of the individual’s microbiome) or as pathogens. In a study to evaluate the role of  Haemophilus parahaemolyticus in human infection and  improve current identification techniques for the organism, Nørskov-Lauritsen et al characterised a collection of H.parahaemolyticus-like bacteria from human clinical specimens, and described this work in a study published in March 20123. Unexpectedly, the collection of strains examined contained a distinct group of strains that could not be allocated to any previously described species. As a consequence, a description of the novel species, Haemophilus sputorum, was included in the 2012 study, then validated as a new species by the IJSEM.

NCTC 13617TNocardia kroppenstedtii (Jones et al. 2014)4

Infection with Nocardia species has been described in the immunosuppressed, those with chronic pulmonary disease and in organ transplant recipients. Symptoms of the primary infection can be pulmonary or in soft tissue, and disseminated forms of infection can occur5. The type strain of Nocardia kroppenstedtii was isolated from a bronchial lavage taken from a lung transplant patient with a pulmonary infection. Earlier this year, in January 2017, BMJ Case Reports published details of the first reported case of disseminated Nocardia kroppenstedtii infection6.

NCTC 13655T - Propionibacterium acnes subsp. elongatum (Dekio et al. 2015)7

NCTC 737, Propionibacterium acnes, is among NCTC’s oldest strains. It was isolated from a severe case of facial acne and accessioned into NCTC in 1920. It had long been documented that the species was composed of three biological variants which showed several differences from each other, and in 2015 Propionibacterium acnes was dissected into two novel subspecies along these lines. Much of this work was undertaken by NCTC scientists. Biovars 1 and 2 were renamed subsp. acnes;  biovar 3 was renamed subsp. elogatum, with the older NCTC 737 and the more recently isolated NCTC 13655 both designated as the type strains of the respective subspecies. NCTC 13655 was isolated from apparently normal facial skin of an atopic dermatitis patient in Japan.

NCTC 13659T - Streptobacillus hongkongensis (Woo et al. 2014)8

Two strains of bacteria, HKU33T and HKU34, were isolated in Hong Kong from two different patients suffering with quinsy and septic arthritis respectively. HKU33 and HKU34 showed similarity to each other through 16S ribosomal RNA gene sequence analysis and partial sequencing of several other genes, but not with other members of the family Leptotrichiaceae or Streptocobacillus moniliformis (the only other validly described species included in the genus Streptobacillus at the time). The novel species Streptobacillus hongkongensis was created to accommodate these two strains and HKU33T was deposited with NCTC in 2014, making it the first valid addition of a species to the genus Streptobacillus since the description of Streptobacillus moniliformis in 1925.


Further reading

Equivalence with bacterial reference strains

Type strains – the most important strains in NCTC?



  1. LPSN. List of prokaryotic names with standing in nomenclature. Available online:
  2. Validation List no. 146. Int. J. Syst. Evol. Microbiol., 2012, 62, 1443-1445
  3. Nørskov-Lauritsen et al., 2012. Identification of haemolytic Haemophilus species isolated from human clinical specimens and description of Haemophilus sputorum sp. nov. International Journal of Medical Microbiology, 302(2), pp.78–83.
  4. Jones et al. 2014. Nocardia kroppenstedtii sp. nov., an actinomycete isolated from a lung transplant patient with a pulmonary infection. Int. J. Syst. Evol. Microbiol., 64, 751-754.
  5. Wilson, J.W., 2012. Nocardiosis: Updates and Clinical Overview. Mayo Clinic Proceedings, 87(4), pp.403–407.
  6. Majeed et al. 2017. First reported case of disseminated Nocardia kroppenstedtii sp nov. infection presenting with brain abscess and endocarditis in an immunocompromised patient with mantle cell lymphoma: challenges in diagnosis and treatment. BMJ Case Rep., 6.
  7. Dekio, I. et al., 2015. Dissecting the taxonomic heterogeneity within Propionibacterium acnes: proposal for Propionibacterium acnes subsp. acnes subsp. nov. and Propionibacterium acnes subsp. elongatum subsp. nov. International journal of systematic and evolutionary microbiology, 65(12), pp.4776–87.
  8. Woo, Patrick C. Y. et al., 2014. Streptobacillus hongkongensis sp. nov., isolated from patients with quinsy and septic arthritis, and emended descriptions of the genus Streptobacillus and Streptobacillus moniliformis. International journal of systematic and evolutionary microbiology, 64(Pt), pp.3034–3039.


January 2020