BACKGROUND This retrospective study was designed to assess risk factors for increased 30-day mortality from bacteremia caused by Escherichia coli or Klebsiella pneumoniae and to calculate the optimal point of time for patients to move from inappropriate empirical antimicrobial therapy to appropriate treatment. MATERIAL AND METHODS This retrospective study analyzed data from 610 patients with a diagnosis of E. coli- and K. pneumoniae-induced bacteremia collected between 2020 and 2023, including population-based information, infection bacteria, comorbidities, and treatment duration. Patients were categorized into 2 groups based on whether they received appropriate empirical antibiotic therapy (AEAT) or inappropriate empirical antibiotic therapy (IEAT). Propensity score-matched (PSM) analysis was performed using 1: 1 nearest neighbor matching. Receiver operating characteristic (ROC) curve analysis determined the time point for patients in the IEAT group to transition to appropriate therapy. RESULTS The study found that 30-day mortality was higher in the IEAT group than in the AEAT group (P=0.043). Multifactorial Cox regression analysis after PSM indicated that Pitt score (P<
0.002), age-adjusted Charlson comorbidity index score (P<
0.002), and inappropriate treatment days (P=0.018) were independent risk factors for increased 30-day mortality. The area under the ROC curve value was 0.613, and the maximum Youden index corresponded to a time turning point of 8 days. CONCLUSIONS Pitt and aCCI scores and inappropriate treatment days are significant risk factors for increased 30-day mortality in patients with E. coli or K. pneumoniae. Timely transition from inappropriate antibiotic to appropriate antibiotic therapy within 8 days was found to improve survival.