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Five NCTC strains used in proficiency testing with aberrant characteristics

The Food and Environmental Proficiency Testing Unit (FEPTU) is responsible for external quality assessment (EQA) schemes where samples of known but undisclosed content are introduced into a laboratory’s routine testing procedure. In the context of laboratories, this provides many benefits including improving the standard of examinations, demonstrating to accreditation bodies, clients and colleagues a commitment to quality and identifying areas where there may be problems.  Additional benefits to staff include giving an insight into their laboratory’s performance, awareness of the impact of incorrect results and knowing how the laboratory compares in performance to others nationally and internationally.

The National Collection of Type Cultures (NCTC) is a repository within the Culture Collections of PHE with over 6000 bacterial strains which are widely available to the many reference laboratories within PHE and external scientific organisations for their processes. NCTC is a dynamic repository and aims to acquire strains of clinical relevance or scientific interest. Five strains used in FEPTU labs in PHE were put into the collection mainly because these were identified as being unique in their characteristics. Knowledge of these unique properties is vital during testing within EQA schemes to avoid reporting of incorrect results.

The five strains in question are NCTC 14202 (Enterococcus faecalis), NCTC 14203 (Escherichia coli), NCTC 14204 (Enterococcus durans), NCTC 14205 (Escherichia coli) and NCTC 14207 (Pseudomonas aeruginosa). These all show aberrant phenotypes and in the case of NCTC 14205 which is a non-lactose fermenter, this is unusual for E. coli. NCTC 14204 which is an Enterococcus would be expected to grow on Enterolert media, but it does not.

For laboratory staff, knowing the specific strains that show different properties is useful in identification within EQA schemes and further ensures the high standards required within these labs are kept. In addition, these strains can be used for validation of new methods, challenging established methods, staff training and as additional controls.


Catalogue No

Current Name

Aberrant phenotypic characteristics

NCTC 14202

Enterococcus faecalis

Weak growth at 37°C and 44°C. No growth on Kanamycin Aesculin Azide agar at 37°C. No growth in Enterolert-E

NCTC 14203

Escherichia coli

Weak B-glucuronidase producer, Maroon colonies on Slanetz and Bartley medium, aesculin negative, identifies as Kluyvera sp. using API profile. Negative for ipaH, aggR, eae, stx1 and stx2 genes

NCTC 14204

Enterococcus durans

Small pink colonies on Slanetz and Bartley medium at 37°C, no growth on Slanetz and Bartley at 44°C, no growth when used in the "Enterolert" detection test

NCTC 14205

Escherichia coli

Does not ferment lactose. Negative for ipaH, aggR, eae, stx1 and stx2 genes

NCTC 14207

Pseudomonas aeruginosa

Small colonies, very weak pigment producer, slow growth on cetrimide agar


Related Links

Proficiency testing for food, water and environmental microbiology


Written by Juandem Agendia

November 2020

November 2020