Emergence of Cefiderocol Resistance During Ceftazidime/avibactam Treatment Caused by a Large Genomic Deletion, Including Ampd and Piucd Genes, in Pseudomonas Aeruginosa.

We report the emergence of cefiderocol resistance during the treatment of a ST312 Pseudomonas aeruginosa respiratory infection with ceftazidime/avibactam. whole genome sequencing (WGS) revealed that resistance was caused by a large genomic deletion, including PiuDC (iron transport system) and AmpD (ampC negative regulator), driven by the integration of phage DNA. Thus, our findings alert that this type of deletion could be an efficient (two mechanisms in one step) specific cefiderocol resistance mechanism that might occur nonspecifically upon treatment with beta-lactams that select for AmpC overexpression.