Claudia Fabrizio, Felice Valzano, Simone Giuliano, Elisabetta Morelli, Daniela Serio, Giovanni Battista Buccoliero, Maurizio Cervellera, Gianfranco La Bella, Fabio Arena, Andrea M. Hujer, Magdalena A. Taracila, Steven Marshall, Robert A. Bonomo, Carlo Tascini
ABSTRACT 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 bla NDM-5 and bla CMY-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.