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Publication Abstract from PubMed

Ceftazidime-avibactam and cefiderocol are two of the latest generation beta-lactam agents that possess expanded activity against highly drug-resistant bacteria, including carbapenem-resistant Enterobacterales Here we show that structural changes in AmpC beta-lactamases can confer reduced susceptibility to both agents. A multidrug-resistant Enterobacter cloacae clinical strain (Ent385) was found to be resistant to ceftazidime-avibactam and cefiderocol without prior exposure to either agent. The AmpC beta-lactamase of Ent385 (AmpC(Ent385)) contained an alanine-proline deletion at positions 294-295 (A294_P295del) in the R2 loop. AmpC(Ent385) conferred reduced susceptibility to ceftazidime-avibactam and cefiderocol when cloned into Escherichia coli TOP10. Purified AmpC(Ent385) showed increased hydrolysis of ceftazidime and cefiderocol compared with AmpC(Ent385Rev), in which the deletion was reverted. Comparisons of crystal structures of AmpC(Ent385) and AmpC(P99), the canonical AmpC of E. cloacae, revealed that the two-residue deletion in AmpC(Ent385) 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 ampC to confer reduced susceptibility to both ceftazidime-avibactam and cefiderocol requires close monitoring.Importance Ceftazidime-avibactam and cefiderocol are newly approved beta-lactam agents that possess broad spectrum activity against multidrug-resistant (MDR) Gram-negative bacteria. We show here that a two amino-acid deletion in the chromosomal AmpC beta-lactamase, identified in a clinical strain of Enterobacter cloacae, confers reduced susceptibility to both agents. By crystallographic studies of free and drug-bound forms of enzyme, we demonstrate that this deletion in AmpC induces slanting of the H-9 helix that is directly connected with the R2 loop, and disappearance of the H-10 helix, is directly responsible for increased hydrolysis of ceftazidime and cefiderocol. These findings provide novel insights into how MDR Gram-negative bacteria may evolve their beta-lactamases to survive selective pressure from these newly developed beta-lactam agents.

Structural basis of reduced susceptibility to ceftazidime-avibactam and cefiderocol in Enterobacter cloacae due to AmpC R2 loop deletion.,Kawai A, McElheny CL, Iovleva A, Kline EG, Sluis-Cremer N, Shields RK, Doi Y Antimicrob Agents Chemother. 2020 Apr 13. pii: AAC.00198-20. doi:, 10.1128/AAC.00198-20. PMID:32284381^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.