Optimizing target inactivation to treat multidrug-resistant <i>Escherichia coli</i> with NDM and PBP3 mutations: “going the extra mile”

A 65-year-old man without identifiable risk factors for multidrug-resistant pathogens was admitted with peritonitis, isolating NDM-producing <i>Escherichia coli</i> from a rectal swab and intraoperative samples. After surgery, ceftazidime-avibactam/aztreonam was administered. Due to poor clinical response, he was switched to imipenem-relebactam/aztreonam, resulting in a successful outcome. Whole-genome sequencing detected <i>bla</i>_NDM-5 and <i>bla</i>_CMY-148 β-lactamases, PBP3 YRIN insertion, and mutated <i>cirA</i> gene. This case illustrates the importance of considering different mechanisms of resistance when choosing combination therapy.