First Comparative Evaluation of Omadacycline, Tigecycline, and Eravacycline Against Carbapenem-Resistant Acinetobacter baumannii and Klebsiella pneumoniae in Beijing Tertiary Teaching Hospital: An in Vitro Broth Microdilution Study

The rising prevalence of carbapenem-resistant organisms (CROs) necessitates the exploration of novel therapeutics options. This study evaluated the in vitro activity and clinical outcomes of three tetracycline-class antibiotics—Eravacycline (ERV), Tigecycline (TGC), and Omadacycline (OMC)—against regional CRO isolates. A total of 233 non-duplicate clinical CRO isolates (106 carbapenem-resistant Klebsiella pneumoniae [CRKP] and 117 carbapenem-resistant Acinetobacter baumannii [CRAB]) were collected from Xuanwu Hospital in 2024. Antimicrobial susceptibility was determined via broth microdilution to measure minimum inhibitory concentrations (MIC), complemented by 0–48 hour time-kill assays. Clinical outcomes of patients treated with TGC or ERV were analyzed. Key findings included: 1. Antimicrobial Potency : ERV demonstrated superior in vitro activity, with MIC ₉₀ values of 0.5 mg/L (ERV), 2 mg/L (TGC), and 4 mg/L (OMC)—4-fold lower than TGC and 8-fold lower than OMC. 2. Time-kill Assays : ERV achieved sustained bactericidal activity at 4–8 × MIC (a novel observation), particularly against CRAB, maintaining >3-log₁₀ CFU/mL reduction for 24–36 hours—2.3-fold longer than TGC and 3.1-fold longer than OMC. While effective against CRKP, ERV demonstrated pathogen-specific advantages for CRAB. 3. Clinical Correlation : The ERV-treated cohort (n = 4) exhibited 0% mortality, compared to TGC-treated patients with 18.9% mortality for CRAB (7/37) and 16.7% for CRKP (4/24). ERV displayed enhanced bactericidal activity and lower resistance thresholds compared to TGC. Preliminary clinical data support its potential as a core therapeutic agent for CRO infections, warranting futher validation in multicenter studies.