Emergence of high-level aztreonam-avibactam and cefiderocol resistance following treatment of an NDM-producing Escherichia coli bloodstream isolate exhibiting reduced susceptibility to both agents at baseline.

mutations. These findings underscore the need for ATM-AVI susceptibility testing for NDM producers, and the potential for PBP3 mutations to confer cross-resistance to ATM-AVI and FDC, which can emerge after CZA-ATM treatment.