Evolution of β-lactamase-mediated cefiderocol resistance

Cefiderocol is a novel siderophore β-lactam with improved hydrolytic stability toward β-lactamases, including carbapenemases, achieved by combining structural moieties of two clinically efficient cephalosporins, ceftazidime and cefepime. Consequently, cefiderocol represents a treatment alternative for infections caused by MDR Gram-negatives.

To study the role of cefiderocol on resistance development and on the evolution of β-lactamases from all Ambler classes, including KPC-2, CTX-M-15, NDM-1, CMY-2 and OXA-48.

Directed evolution, using error-prone PCR followed by selective plating, was utilized to investigate how the production and the evolution of different β-lactamases cause changes in cefiderocol susceptibility determined using microbroth dilution assays (MIC and IC50).

We found that the expression of blaOXA-48 did not affect cefiderocol susceptibility. On the contrary, the expression of blaKPC-2, blaCMY-2, blaCTX-M-15 and blaNDM-1 substantially reduced cefiderocol susceptibility by 4-, 16-, 8- and 32-fold, respectively. Further, directed evolution on these enzymes showed that, with the acquisition of only 1-2 non-synonymous mutations, all β-lactamases were evolvable to further cefiderocol resistance by 2- (NDM-1, CTX-M-15), 4- (CMY-2), 8- (OXA-48) and 16-fold (KPC-2). Cefiderocol resistance development was often associated with collateral susceptibility changes including increased resistance to ceftazidime and ceftazidime/avibactam as well as functional trade-offs against different β-lactam drugs.

The expression of contemporary β-lactamase genes can potentially contribute to cefiderocol resistance development and the acquisition of mutations in these genes results in enzymes adapting to increasing cefiderocol concentrations. Resistance development caused clinically important cross-resistance, especially against ceftazidime and ceftazidime/avibactam.