Structural Basis of Reduced Susceptibility to Ceftazidime-Avibactam and Cefiderocol in Due to AmpC R2 Loop Deletion.

Ceftazidime-avibactam and cefiderocol are two of the latest generation β-lactam agents that possess expanded activity against highly drug-resistant bacteria, including carbapenem-resistant Here, we show that structural changes in AmpC β-lactamases can confer reduced susceptibility to both agents. A multidrug-resistant clinical strain (Ent385) was found to be resistant to ceftazidime-avibactam and cefiderocol without prior exposure to either agent. The AmpC β-lactamase of Ent385 (AmpC) contained an alanine-proline deletion at positions 294 and 295 (A294_P295del) in the R2 loop. AmpC conferred reduced susceptibility to ceftazidime-avibactam and cefiderocol when cloned into TOP10. Purified AmpC showed increased hydrolysis of ceftazidime and cefiderocol compared to AmpC, in which the deletion was reverted. Comparisons of crystal structures of AmpC and AmpC, the canonical AmpC of complex, revealed that the two-residue deletion in AmpC induced drastic structural changes of the H-9 and H-10 helices and the R2 loop, which accounted for the increased hydrolysis of ceftazidime and cefiderocol. The potential for a single mutation in to confer reduced susceptibility to both ceftazidime-avibactam and cefiderocol requires close monitoring.