18 Dec 2023:
Colistin susceptibility testing
A few weeks ago, we informed EUCAST users, that the Warning against
bioMerieux AST material for colistin, still stands. The item referred
(by a link) to the EUCAST Warnings page where it was made clear exactly
which material was malfuntioning and should have been withdrawn by
bioMerieux. However, the news item itself was not sufficiently specific.
Following contact with bioMerieux and Liofilchem and also with
colleagues asking questions, we would like to modify the item as
follows:
Malfunctioning colistin gradient tests
Colistin gradient tests sold by bioMerieux (Etest) and Liofilchem
(MTS) for susceptibility testing (AST) have been malfunctioning since
the very beginning. It is 7 years since it was conclusively shown that
both colistin gradient tests completely fail to meet acceptable
accuracy, especially on values close to the breakpoint. The warning
was first published in 2016 and has been reviewed and retained several
times by EUCAST in the period 2016 – 2023. Liofilchem informed us in the
spring of 2023 that their gradient test was for ROU (research use only)
and should not be used for clinical susceptibility testing. EUCAST has
now been informed by
bioMerieux that their product will no longer be available after the 1st
quarter 2024.
A new colistin test on VITEK2 cards has been developed by bioMerieux
and we are now frequently asked by colleagues about the performance.
EUCAST never evaluated Vitek2 or any other semiautomated AST system - it
is beyond our capacity to systematically review
material and methods other than that which is part of EUCAST standard
methods. We encourage users to ask to see the full evaluations performed
by the companies (species, broth microdilution MIC-values, Vitek2
results) to make sure that sufficient and relevant species and
strains/isolates with reference MIC values on or close to the
breakpoints (2 mg/L for all Enterobacterales, 4 mg/L for Pseudomonas
aeruginosa) were used in the validation. We also encourage colleagues to
report problems both to the manufacturer and to
EUCAST.
We apologize for any misunderstanding which could have occurred if readers did not go to the full text.
