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NCTC: a dynamic collection with bla bla bla…....

NCTC must endure as a dynamic collection of bacteria, accessible and significant to the biomedical scientific community. With this objective in mind we have recently added five new strains that can be used as positive controls for detecting beta-lactamase genes: blaGES-5, blaSME-4, blaSPM-1, blaNMC-A and blaIMI-2. We also offer two new strains for detecting genes conferring transferable resistance to the oxazolidinone class including both linezolid and tedizolid.

The study of antimicrobial resistance is long-associated with NCTC. Naomi Datta was one of the first scientists to explain the mechanism for the spread of antimicrobial resistance in Enterobacteriaceaein the 1960’s.  She was an eminent NCTC Consultant, instrumental in bringing the Murray Collection of pre-antibiotic era Enterobacteriaceae strains to NCTC in 1980. As antimicrobial resistance has emerged as one of the greatest public health challenges in the 21st century, it is fitting that NCTC scientists continue to work closely with colleagues in the PHE National Infection Service Antimicrobial Resistance and Healthcare Associated Infections (AMRHAI) Reference Unit to provide strains for microbiologists working in this important field.  

The AMRHAI Reference Unit, under the leadership of Professor Neil Woodford, an international expert in molecular detection of the genetic determinants of key resistances, is ideally placed to identify the bacterial strains that are the most appropriate controls for detecting resistance mechanisms. This expertise is complemented by that of the NCTC team, which is highly proficient at managing and supplying bacteria to the global community, ensuring that the microorganisms remain authentic and are distributed safely in compliance with all the regulations applying to biological materials.

The genetic basis for antimicrobial resistance includes acquisition and expression of new genes by horizontal transfer or mutations in genes that affect gene expression.  Beta-lactamases are enzymes that can inactivate beta-lactam antibiotics and the bla gene refers to the gene that confers this resistance. Organisms expressing blaGES-5, blaSME-4, blaSPM-1, blaNMC-A and blaIMI-2 belong to the carbapenemase family and are carbapenem-hydrolysing β-lactamases, which inactivate penicillins, cephalosporins and carbapenems through hydrolysis. There are multiple kits for detecting an array of bla genes and it is essential that control strains are available so laboratories can evaluate and validate those rapid detection methods.

Linezolid is a relatively new synthetic antimicrobial that has been available since 2000 and which inhibits protein synthesis. It has been effective in the treatment of common Gram positive pathogens such as Staphylococcus aureusEnterococcus spp. and Streptococcus pneumoniae, all of which are now becoming increasingly resistant. Molecular detection methods for linezolid resistance are now available which means that suitable control strains are becoming an essential tool in clinical microbiology laboratories.


Strains available form NCTC

NCTC Number

Organism Name

Resistance Gene


Escherichia coli GES-5

Positive control for detection of blaGES-5


Serratia marcescens SME-4

Positive control for detection of blaSME-4


Pseudomonas aeruginosa SPM-1

Positive control for detection of blaSPM-1


Enterobacter cloacae complex  NMC-A

Positive control for detection of blaNMC-A


Enterobacter cloacae complex  IMI-2

Positive control for the detection of blaIMI-2


Enterococcus faecium optrA

Positive control for the detection of optrA conferring resistance to linezolid and phenicols


Staphylococcus epidermidis  cfr (also contains G2576T 23S rRNA mutation)

Positive control for the detection of cfr or G2576T mutation (both confer resistance to linezolid)




Datta, N., & Kontomichalou, P. (1965). Penicillinase synthesis controlled by infectious R factors in Enterobacteriaceae. Nature, 208(5007), 239-41.


January 2020