Optimizing target inactivation to treat multidrug-resistant Escherichia coli 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 Escherichia coli 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 blaNDM-5 and blaCMY-148 β-lactamases, PBP3 YRIN insertion, and mutated cirA gene. This case illustrates the importance of considering different mechanisms of resistance when choosing combination therapy.