Clonal lineage and biofilm growth shape cefiderocol activity in Acinetobacter baumannii from oncology patients

Introduction: isolates. Methods: from oncology patients underwent whole-genome sequencing and multilocus sequence typing. Cefiderocol activity was quantified in planktonic and biofilm-associated states using minimum bactericidal concentration (MBC) and minimum biofilm eradication concentration (MBEC) assays. Results: was detected exclusively in ST2. Colistin and cefiderocol were the most active agents overall. ST2 strains showed higher cefiderocol MBC values than NST strains. However, avibactam significantly reduced cefiderocol MBC in ST2, consistent with class D β-lactamases activity. ST2 and NST isolates exhibited comparable distributions of iron acquisition genes and similar CAS-detected siderophore activity under the assay conditions tested. Cefiderocol activity was significantly reduced in biofilms relative to planktonic cells (median MBEC 2 µg/ml versus median MBC 0.5 µg/ml). NST exhibited higher MBEC/MBC ratios than ST2 isolates, indicating greater biofilm-associated tolerance to cefiderocol. Discussion: carriage and higher cefiderocol bactericidal thresholds and show that cefiderocol activity is consistently reduced in the biofilm state. Future studies integrating functional measures of iron acquisition and β-lactamase activity will be needed to define the determinants of cefiderocol efficacy across lineages and growth states.