Aztreonam–Avibactam Susceptibility and Genomics of NDM-Producing Escherichia coli in Pediatric Patients from Gaza and Qatar

Background: Aztreonam–avibactam (ATM/AVI) emerges as a promising treatment for pediatric infections caused by New Delhi metallo-beta-lactamase (NDM)-producing Escherichia coli once approved for children aged ≤18 years. Methods: We assessed in vitro susceptibility to ATM/AVI and characterized the molecular resistance mechanisms in NDM-producing E. coli recovered from admission rectal screening swabs of war-affected Palestinian children (December 2023–July 2024) and children in Sidra Medicine’s catchment population in Doha (January 2022–December 2025). Minimum inhibitory concentrations (MICs) were determined using the MIC Test Strip method and interpreted according to the European Committee on Antimicrobial Susceptibility Testing breakpoints. Penicillin-binding protein 3 (PBP3) insertions and the co-production of CMY-type plasmid-mediated AmpC beta-lactamases (pAmpC) were characterized by short-read whole-genome sequencing. Linear regression estimated mean differences in log2-transformed MICs by PBP3 insertion and CMY status. Results: A total of 74 non-duplicate NDM-producing E. coli isolates were analyzed, of which 69 (93.2%) produced NDM-5. Overall, 18 (24.3%) isolates exhibited resistance to ATM/AVI (MIC > 4 mg/L). Sixty-six (89.2%) isolates harbored PBP3 insertions, comprising YRIN (48 isolates; 64.9%), mainly detected in ST167, and YRIK (18 isolates; 24.3%), mainly detected in ST405. CMY-42 (17 isolates) and CMY-145 (eight isolates) were exclusively identified in isolates concurrently harboring PBP3 insertions. ATM/AVI log2 MICs were significantly higher in isolates harboring PBP3 insertions, particularly YRIK, and increased further when combined with CMY-42 or CMY-145. Conclusions: Our study reveals a high proportion of NDM-producing E. coli belonging to high-risk clones harboring PBP3 mutations, either alone or in combination with CMY-type pAmpC, driving substantial increases in ATM/AVI MICs across two distinct Middle Eastern pediatric cohorts. Large-scale regional genomic surveillance is needed to determine the extent of convergent resistance mechanisms associated with reduced susceptibility to ATM/AVI and other newer β-lactams targeting PBP3.