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

Abstract 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 with fewer treatment failures due to AmpC overproduction (adjusted hazard ratio, 0.5 [95% CI, .2–.9]). However, compared to cefepime/carbapenems, using third-generation cephalosporins as definitive therapy remained associated with this adverse outcome (15% vs 1%).