Resistance to Cefiderocol Involved Expression of PER-1 β-Lactamase and Downregulation of Iron Transporter System in Carbapenem-Resistant Acinetobacter baumannii

Cefiderocol (CFDC) is a promising antimicrobial agent against multidrug resistant Gram-negative bacteria. However, CFDC resistance has emerged in carbapenem-resistant (CR-AB) but the underlying mechanisms remain unclear. Whole-genome sequencing and transcriptome sequencing were performed on CFDC-non-susceptible and CFDC-susceptible isolates. Two different recombinant plasmids was electro-transformed into the BL21 strain to determine the impact of and the combined impact of and on CFDC resistance. Fifty-five CR-AB isolates with minimum inhibitory concentrations (MICs) ranged from 0.06 mg/L to >256 mg/L were sequenced, including 47 CFDC-non-susceptible and eight CFDC-susceptible isolates. Two CFDC-non-susceptible isolates belonged to ST104 whereas the remaining isolates belonged to ST2, and was present only in CFDC-non-susceptible isolates. Amino acid substitutions were noted in penicillin-binding proteins (PBPs) in four CFDC-susceptible isolates, with slightly elevated MICs. The MICs of recombinant BL21 carrying the gene increased 64-fold and recombinant BL21 carrying both the and genes increased 8-fold but both remained within the susceptibility range. Transcriptome sequencing of 17 CFDC-non-susceptible isolates and eight CFDC-susceptible isolates revealed that transcriptional levels of various iron transport proteins, such as , and , and the energy transduction system, TonB-ExbB-ExbD, were relatively downregulated in CFDC-non-susceptible isolates. GO enrichment analysis revealed that the upregulated genes in CFDC-non-susceptible isolates were mainly associated with redox homeostasis and stress response. Besides, the expression levels of the and exbD genes were negatively correlated with the MICs. PER-1 production, iron transport system downregulation, and mutations in PBPs may synergistically impart high-level resistance to CFDC in CR-AB.