This warning, specifically targeting the failure of colistin gradient tests to provide the correct MIC, was initially issued July 2016 and updated 26 June, 2017 and is extended and still valid November 2023. bioMerieux has now (2025) stopped the production and all sales of colistin Etest. Liofilchem on the other hand still produces the colistin MTS but have since more than a year, removed the IVD label and introduced an RoU (Research Only) label which means it should not be used in clinical laboratories for predicting colistin susceptibility in bacteria. So, whatever use there is for colistin gradient tests, it is certainly not related to clinical microbiology.
In 2024 (August), the producer of UMIC Colistin (Bruker Daltonics GmbH & Co), issued a warning against the use of their colistin test and informed users and authorities of the failure of specific lots of the product: 240410COL, 240418COL, 240506COL. EUCAST has now been informed that the failing lots have been withdrawn and that users have been informed to not use the listed lots of the product. According to Bruker Daltonics more recent lots are not affected. These incidents point to the importance of producer and laboratory quality control.