AST of bacteria

EUCAST warnings concerning antimicrobial susceptibility testing products or procedures.

The EUCAST Development Laboratories, from time to time discover products (disks, media batches, gradient tests, devices and/or procedures) which are not performing to the expected standard. When this is the case we inform the manufacturer and publish a warning on this page.

We do not systematically test all products so the lack of a warning does not imply that there is no problem with the product in question.

Laboratories which experience problems with a susceptibility test method, and suspect that this may be related to a particular product, may contact EUCAST for advice.


1. Warnings against piperacillin-tazobactam gradient tests from two manufacturers removed. 
Warnings against Etest and MTS were removed November 2019 and April 2020, respectively.
Note. The new Etest and MTS for piperacillin-tazobactam are valid only for Enterobacterales, Pseudomonas aeruginosa and Acinetobacter - and should not be used with other bacteria, such as Bacteroides or Haemophilus without having confirmed with the manufacturers. 

2. Wide variation in disk quality in 16 disks from nine manufacturers - this warning was issued in 2015 and reiterated 2016 and 2017. There is new information on improved quality November 23, 2017 (see document). 

3. Problems with colistin susceptibility testing and several commercially available products - the warning initially issued July 2016 was updated 26 June, 2017 and is extended and still valid May 2020.

4. Vancomycin susceptibility testing in Enterococcus faecalis and E. faecium 
using MIC gradient tests
a modified warning; 21 May, 2019.

5. A problem with meropenem in a Thermofisher Sensititre panel (DKMGN) discovered
(6 November, 2018)

6. Variable performance of the itraconazole agar in the azole resistance screening
plate from VipCheckTM
  (13 December, 2018). The problem has now been solved, the affected batches are no longer available, and the warning withdrawn (11 March, 2021) For further clarification, contact the EUCAST AFST.  

7. Warning against the use of gradient tests for determining
benzylpenicillin MICs in S. pneumoniae
​​​​​​​(21 November, 2019; data and data analysis added 27 November; updated 4 May 2022).
bioMerieux has added a "Follow-up information to customers" on this issue. 
There is no further information from either company to indicate product development. The EDL is now conducting further tests (January, 2022).
Please observe, that the 8 mm cut-off mentioned in the document, since then has been changed to 9 mm (see breakpoint table v 12.0).

8. Mueller-Hinton media - EUCAST has evaluated 21 brands of commercially available MH powders, not the factory produced plates (29 February, 2020).

9. Mueller-Hinton pre-poured media - EUCAST has now evaluated commercially available pre-poured MH plates. Results will be available soon.

10. Cefiderocol MIC by broth microdilution on freeze dried panels from Thermofisher - the manufacturer has issued a warning against all current batches of MH broth when used together with any freeze dried Sensititre BMD panel.
The following plates are listed as containing cefiderocol, MDRGNX2F, CAN2MSTF, GNARUM6F, THAMDR1F, CMP3QLN, DEURUB1, SWEEDL1, EUSHION8, FRCNRP4 and the manufacturer issues the following recommendation: "If you have bought any of these lots, then please ignore results for Cefiderocol". EUCAST recommends, If uncertain confirm directly with the manufacturer (January, 2022),




Warnings will be modified or removed when the issues have been solved.