In Vitro Activity of Cefiderocol, a Siderophore Cephalosporin, against Multidrug-Resistant Gram-Negative Bacteria

Cefiderocol is a parenteral siderophore cephalosporin with a catechol-containing 3' substituent. We evaluated its MICs against Gram-negative bacteria, using iron-depleted Mueller-Hinton broth. The panel comprised 305 isolates of Enterobacterales, 111 of Pseudomonas aeruginosa, and 99 of Acinetobacter baumannii, all selected for carbapenem resistance and multidrug resistance to other agents. At 2 and 4 mu g/ml, cefiderocol inhibited 78.7 and 92.1%, respectively, of all Enterobacterales isolates tested, with rates of 80 to 100% for isolates with all modes of carbapenem resistance except NDM enzymes (41.0% inhibited at 2 mu g/ml and 72.1% at 4 mu g/ml) or combinations of extended-spectrum beta-lactamase (ESBL) and porin loss (61.5% inhibited at 2 mu g/ml and 88.5% at 4 mu g/ml). Cefiderocol also inhibited 81.1 and 86.5% of all P. aeruginosa isolates at 2 and 4 mu g/ml, respectively, with rates of 80 to 100% for isolates with VIM, IMP, GES, or VEB beta-lactamases and slightly lower rates for those with NDM (45.5% at 2 mu g/ml and 72.7% at 4 mu g/ml) and PER (66.7% at 2 mu g/ml and 73.3% at 4 mu g/ml) enzymes; 63.3% of P. aeruginosa isolates were inhibited at the FDA's 1-mu g/ml breakpoint. Lastly, cefiderocol at 2 and 4 mu g/ml inhibited 80.8 and 88.9% of the A. baumannii isolates, respectively, with rates of >85% for isolates with OXA-51-like,-23,-24, or -58 enzymes and 50% at 2 mu g/ml and 80% at 4 mu g/ml for those with NDM carbapenemases. Dipicolinic acid and avibactam weakly potentiated cefiderocol against Enterobacterales isolates with metallo-beta-lactamases (MBLs) and serine carbapenemase, respectively, indicating incomplete beta-lactamase stability.