| Summary: | The Gram-negative bacilli <i>Serratia</i> spp., <i>Providencia</i> spp., <i>Morganella morganii</i>, <i>Citrobacter freundii</i> complex, <i>Enterobacter</i> spp. and <i>Klebsiella aerogenes</i> are common Enterobacterales that may harbor inducible chromosomal AmpC beta-lactamase genes. The purpose of the present study was to evaluate treatment outcomes and identify predictors of early treatment response in patients with bloodstream infection caused by potential AmpC beta-lactamase-producing Enterobacterales (SPICE-BSI). This cohort study included adult patients with SPICE-BSI hospitalized between 01/2011 and 02/2019. The primary outcome was early treatment response 72 h after the start of active treatment, defined as survival, hemodynamic stability, improved or stable SOFA score, resolution of fever and leukocytosis and microbiologic resolution. Among 295 included patients, the most common focus was the lower respiratory tract (27.8%), and <i>Enterobacter</i> spp. (<i>n</i> = 155) was the main pathogen. The early treatment response rate was significantly lower (<i>p</i> = 0.006) in the piperacillin/tazobactam group (17/81 patients, 21.0%) than in the carbapenem group (40/82 patients, 48.8%). Independent negative predictors of early treatment response (<i>p</i> < 0.02) included initial SOFA score, liver comorbidity and empiric piperacillin/tazobactam treatment. In vitro piperacillin/tazobactam resistance was detected in three patients with relapsed <i>Enterobacter</i>-BSI and initial treatment with piperacillin/tazobactam. In conclusion, our findings show that piperacillin/tazobactam might be associated with early treatment failure in patients with SPICE-BSI.
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