Colistin (polymyxin E) MIC determination is associated with several methodological issues. The CLSI-EUCAST joint Polymyxin Breakpoints Working Group recommend that only broth microdilution is suitable for determining Colistin MIC .
EUCAST has issued warnings about batches of gradient diffusion products
MICRONAUT's broth microdilution Colistin MIC has been on the market for many years and conforms to ISO20776-1:2006. The strip comes in packs of 5 plates, each plate has 8 removable strips of 12 wells, giving each pack 40 tests.
from the EUCAST website Summary of results for all commercial BMD methods Essential agreement (MICs within ± 1 dilution of reference MIC):