Clinical Evolution of AmpC-Mediated Ceftazidime-Avibactam and Cefiderocol Resistance in Enterobacter cloacae Complex Following Exposure to Cefepime

We report 2 independent patients from whom carbapenem and ceftazidime-avibactam-resistant Enterobacter cloacae complex strains were identified. The ceftazidime-avibactam resistance was attributed to a 2-amino acid deletion in the R2 loop of AmpC beta-lactamase, which concurrently caused resistance to cefepime and reduced susceptibility to cefiderocol, a novel siderophore cephalosporin.