Cefiderocol – An effective antimicrobial for MDR infections but a challenge for routine antimicrobial susceptibility testing

Cefiderocol is a novel cephalosporin-siderophore conjugate antibiotic that holds promise to thwart infections caused by multi-drug-resistant gram-negative bacilli. Its antibacterial activity against normally susceptible species is not affected by most β-lactamases, including metallo-β-lactamases. Due to the siderophore-mediated entry into the cell, the activity of cefiderocol is less affected by porin loss or active efflux resistance than many other β-lactam antibiotics. The aim of this study was to assess in vitro susceptibility to the cefiderocol of carbapenemase-producing gram-negative bacilli from clinical samples of hospitalized patients. We analyzed 102 clinical strains of carbapenemase-producing Enterobacterales and non-fermentives from hospital centers in Łódź, Poland. Antimicrobial susceptibility to cefiderocol was tested by the minimum inhibitory concentration test strips and disc diffusion methods. The obtained results turned out to be ambiguous, and the area of technical uncertainty made their interpretation very difficult. The cost of therapy with this antibiotic, and difficulties in interpreting the drug susceptibility are the limitations to the use of cefiderocol. Intensive work should be carried out to finally standardize an easily accessible and reliable method for the determination of susceptibility to cefiderocol.