Mutation rate of AmpC-β-lactamase-producing Enterobacterales and treatment in clinical practice: A word of caution.

In a retrospective multicenter study of 575 patients with bloodstream infections or pneumonia due to wild-type AmpC β-lactamase-producing Enterobacterales, species with low in-vitro mutation rates for AmpC derepression were associated to fewer treatment failures due to AmpC overproduction (aHR 0.5, 95%CI 0.2-0.9). However, compared to cefepime/carbapenems using 3GC as definitive therapy remained associated with this adverse outcome (15% vs. 1%).