Control strains
UK Standards for Microbiology Investigations (UK SMIs) are a comprehensive referenced collection of recommended algorithms and procedures for clinical microbiology.
The UK SMIs include a series of Test Procedures (TPs) that are used in clinical testing laboratories throughout the UK and also further afield. The TPs describe commonly undertaken tests and include recommended control strains from NCTC. The use of controls provides essential information about the validity of the test results.
It is important that laboratories use control strains from recognised sources to ensure that the strains are fully characterised and authentic this also helps standardise the quality of testing across the country. Laboratories frequently prepare in house reference stocks of the control strains for daily use. Those reference stocks must be managed carefully to ensure the strains are not sub-cultured (passaged) too frequently because this may lead to genetic variation and/or contamination.
The UK Health Security Agency (UKHSA) in conjunction with its partner organisations develops SMIs to help to assure equivalence of investigation strategies in different laboratories; all the SMI Test Procedures (TPs) for bacteriology stipulate the use of control strains from the National Collection of Type Cultures (NCTC). Controls are necessary to help demonstrate that laboratory procedures are being operated and interpreted correctly.
You can view the UK Standards for Microbiology Investigations document to see example reference strains for UK Standards for Microbiology Investigations test procedures. For further information or to download any of the Standards for Microbiological Investigations go to the UKHSA’s UK Standards for Microbiology Investigations webpage.
Culture Collections now provide a cost effective means for clinical microbiology laboratories to update their stock cultures of the 17 NCTC strains needed for the SMI TPs in a single order. The SMI TP NCTC set includes controls listed below.
|
UK SMI |
Example reference strain for both phenotypic and EUCAST disc susceptibility tests |
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|---|---|---|---|---|
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Bacteria |
Alternative bacteria |
Fungi |
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Positive control Negative control |
Enterococcus faecalis NCTC 12697 Streptococcus agalactiae NCTC 8181 |
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Positive control Negative control |
N/A **
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Positive control Negative control |
Streptococcus pneumoniae NCTC 12977 Streptococcus mitis NCTC 10712 |
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Positive control Negative control |
Staphylococcus aureus NCTC 6571 Streptococcus mitis NCTC 10712 |
Staphylococcus aureus NCTC 12973
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Cryptococcus neoformans NCPF 3168
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Positive control Negative control |
Staphylococcus aureus NCTC 6571 Staphylococcus haemolyticus NCTC 11042
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Staphylococcus aureus NCTC 12973
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Positive control Negative control |
Staphylococcus aureus NCTC 6571 Staphylococcus haemolyticus NCTC 11042 |
Staphylococcus aureus NCTC 12973
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Positive control Negative control |
Escherichia coli NCTC 10418 Proteus mirabilis NCTC 10975 |
Escherichia coli NCTC 12241
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Positive control Negative control |
Proteus mirabilis NCTC 10975 Acinetobacter lwoffii NCTC 5866 |
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TP 24 - ONPG (ß-Galactosidase) test (for Enterobacteriaceae) |
Positive control Negative control |
Escherichia coli NCTC 10418 Proteus mirabilis NCTC 10975 |
Escherichia coli NCTC 12241
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Positive control Negative control |
Neisseria lactamica NCTC 10617 Neisseria gonorrhoeae NCTC 8375 |
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Positive control Negative control |
Streptococcus pneumoniae NCTC 12977 Streptococcus mitis NCTC 10712 |
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Positive control Negative control |
Pseudomonas aeruginosa NCTC 10662 Escherichia coli NCTC 10418 |
Pseudomonas aeruginosa NCTC 12903
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Candida albicans NCPF 3281
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TP 27 - Oxidation/fermentation of glucose test (Gram negative roots)
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Oxidation: Positive control Negative control |
Pseudomonas aeruginosa NCTC 10662 Acinetobacter Iwoffii NCTC 5866 |
Pseudomonas aeruginosa NCTC 12903
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Fermentation: Positive control Negative control |
Escherichia coli NCTC 10418 Acinetobacter Iwoffii NCTC 5866 |
Escherichia coli NCTC 12241
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TP 27 - Oxidation/fermentation of glucose test (Gram positive cocci)
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Oxidation: Positive control Negative control |
Micrococcus luteus NCTC 2665
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Fermentation: Positive control Negative control |
Staphylococcus aureus NCTC 6571 OF basal medium without carbohydrate |
Staphylococcus aureus NCTC 12973
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Positive control Negative control |
Haemophilus parainfluenzae NCTC 10665 Haemophilus influenzae NCTC 11931 |
Haemophilus influenzae NCTC 12975
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Positive control Negative control |
Escherichia coli NCTC 10418 Staphylococcus aureus NCTC 6571 |
Escherichia coli NCTC 12241
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Positive control Negative control |
N/A** |
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Positive control Negative control |
Staphylococcus aureus NCTC 6571 Staphylococcus haemolyticus NCTC 11042 |
Staphylococcus aureus NCTC 12973
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Positive control Negative control |
Proteus mirabilis NCTC 10975 Escherichia coli NCTC 10418 |
Escherichia coli NCTC 12241
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Cryptococcus neoformans NCPF 3168
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X and V factor |
Haemophilus influenzae NCTC 11931 |
Haemophilus influenzae NCTC 12975
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V factor only |
Haemophilus parainfluenzae NCTC 10665 |
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X factor only |
Haemophilus haemoglobinophilus NCTC 8540 |
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Positive control Negative control |
Use the recommended controls within this document. However, if controls used are other than those recommended, laboratories should ensure that these are validated prior to use. |
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Positive control Negative control |
The quality control organisms used is dependent on what the manufacturer provides. Follow manufacturer’s instructions. Laboratories should include their own validated positive and negative controls. |
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*The reference bacterial strains have not been validated by NCTC for the test shown.
**N/A – Not Applicable
*** The reference fungal strains have not been validated by NCTC for the tests at the time of publication.
There is validation data for all the strains tested.
Those listed as “alternative strains” in this table are also EUCAST control strain, and are suitable for use for both purposes.
Following several high profile cases in 2012, the Department of Health, in collaboration with the Health Protection Agency, issued advice to healthcare providers to assist in the control of potential infection from taps and water systems. This is of particular significance in augmented care units (high dependency, adult, paediatric and neonatal critical care, renal, transplant, haemato-oncology and burns units).
The guidance now forms 'Part C' of Health Technical Memorandum 04-01: Safe water in healthcare (2016). It includes guidance on best practice for the microbiological examination of water samples for P. aeruginosa.
The use of reference materials as control strains is key in microbiological examinations:
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to validate methods and confirm that they are fit for their intended purpose
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to confirm that laboratories can properly operate methods before introducing them
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for quality control procedures for on-going monitoring of tests and calibrations
NCTC offer a range of control strains of Pseudomonas species cited by the World Data Centre for Micro-organisms (WDCM) as follows:
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WDCM Ref |
NCTC No. |
Species |
|---|---|---|
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WDCM 00024 |
Pseudomonas aeruginosa |
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WDCM 00025 |
Pseudomonas aeruginosa |
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WDCM 00026 |
Pseudomonas aeruginosa |
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WDCM 00114 |
Pseudomonas aeruginosa |
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WDCM 00115 |
Pseudomonas fluorescens |
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WDCM 00116 |
Pseudomonas fragi |
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WDCM 00117 |
Pseudomonas putida |
Antimicrobial Resistance (AMR) in N. gonorrhoeae is of significant international concern. Several high profile bodies (ECDC, CDC, WHO) have issued both global and regional action plans which aim to ensure that gonorrhoea remains a treatable infection. A consistent theme within of all the recommendations is the strong emphasis on AMR surveillance of N. gonorrhoeae isolates to monitor regional trends and to detect new and emerging resistance. However, the lack of a gold standard phenotypic AMR method for N. gonorrhoeae can present a challenge for laboratories and also make data comparisons between different laboratories difficult.
In order to address this, a set of 14 well-characterised WHO N. gonorrhoeae reference strains have been described and deposited within NCTC by Dr. Magnus Unemo from the WHO Collaborating Centre in Orebro, Sweden. This panel contains strains which display examples of all sensitive and resistant phenotypes to antimicrobials (current and historic) that have been used to treat gonorrhoea. All the strains have full reference genomes available and have been extensively characterised (MLST, NG-MAST type, plasmid status etc.). It is envisaged that they will be invaluable quality control strains for any laboratory undertaking either molecular diagnostics and/or AMR testing on N. gonorrhoeae isolates for surveillance or individual patient management purposes.
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NCTC No. |
Current Name |
Other Names |
Isolated From |
Type Strain |
|---|---|---|---|---|
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Neisseria gonorrhoeae |
WHO F |
Isolated in Canada, 1991 |
No |
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Neisseria gonorrhoeae |
WHO G |
Isolated in Thailand, 1997 |
No |
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Neisseria gonorrhoeae |
WHO K |
Isolated by Dr. T. Muratani |
No |
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Neisseria gonorrhoeae |
WHO L |
Isolated in Asia, 1996 |
No |
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Neisseria gonorrhoeae |
WHO M |
Isolated in the Philippines, 1992 |
No |
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Neisseria gonorrhoeae |
WHO N |
Isolated in Australia, 2001 |
No |
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Neisseria gonorrhoeae |
WHO O |
Isolated in Canada, 1991 |
No |
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Neisseria gonorrhoeae |
WHO P |
No |
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Neisseria gonorrhoeae |
WHO U |
Clinical isolate. Human woman, pharyngeal specimen. Sweden, May 2011 |
No |
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Neisseria gonorrhoeae |
WHO V |
Clinical isolate. Human, urethral specimen from case of urethritis. Karlstad, Sweden, 2012 |
No |
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Neisseria gonorrhoeae |
WHO W |
Clinical Isolate. Human. Hong Kong, 2007 |
No |
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Neisseria gonorrhoeae |
WHO X |
Clinical isolate. Human female, pharynx. Kyoto, Japan, 2009 |
No |
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Neisseria gonorrhoeae |
WHO Y |
Clinical isolate. Human, 50yr old male, urethral specimen. Quimper, France, June 2010. |
No |
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Neisseria gonorrhoeae |
WHO Z |
Clinical isolate. Human, female, genital swab. Australia, 2013. |
No |