Cefiderocol susceptibility testing

Warning issued concerning cefiderocol susceptibility testing: there is currently no commercially available functioning test for cefiderocol MIC determination. EUCAST has investigated those available and all have problems with accuracy, reproducibility, bias and/or for some, with skipped wells. For this reason there is no easy way to resolve the susceptibility interpretation of isolates in the ATU (area of technical uncertainty). These are the recommendations of EUCAST until the issue of MIC determination is solved./June 2022:

  • EUCAST recommends laboratories to start testing cefiderocol with disk diffusion. Resistance to betalactam agents is increasing and therapeutic alternatives are few. Disk diffusion, when correctly performed and calibrated using quality material and recommended quality control guidelines, is predictive of susceptibility and resistance outside the ATU.
  • Inside the ATU, when there is no alternative method to resolve interpretative uncertainties (eg MIC-testing in the routine laboratory or acquiring assistance from a reference laboratory), EUCAST recommend colleagues to ignore the ATU and interpret using the zone diameter breakpoints in the breakpoint table.
  • Templates for disk diffusion proficiency assessment are available here.