Unexpected in vivo activity of ceftazidime alone and in combination with avibactam against New Delhi metallo-β-lactamase-producing Enterobacteriaceae in a murine thigh infection model.

The emergence of the New Delhi metallo-β-lactamase (NDM) among Enterobacteriaceae has become a global concern because of its high levels of in vitro resistance to nearly all available antibiotics. However, recent in vivo studies demonstrated the efficacies of carbapenems against NDM-1-producing isolates despite high MICs. Herein, we report in vivo findings with ceftazidime and ceftazidime-avibactam against an isogenic pair (wild type and NDM-1) and four clinical NDM-producing isolates that demonstrate discordance between MICs measured in vitro and the in vivo activity of ceftazidime-avibactam against this resistant genotype.