Six Years of Acinetobacter Species in Critical Care: Carbapenem Resistance and Non-Susceptibility, Clinical Outcomes, and Lessons for Stewardship

<b>Background</b>: <i>Acinetobacter</i> spp., particularly <i>A. baumannii</i>, is a major intensive care unit (ICU) pathogen frequently associated with carbapenem non-susceptibility and delayed initiation of receipt of therapy. <b>Methods</b>: We conducted a single-center retrospective ICU cohort study in Romania (January 2019-December 2024) of adults with clinical cultures positive for <i>Acinetobacter</i> spp. (first isolate per patient). Susceptibility was interpreted per EUCAST. We assessed species distribution, carbapenem non-susceptibility, receipt of at least one in vitro active empiric agent, time to active therapy (TTAT, from index culture collection), early inflammatory biomarkers [neutrophile-to-lymphocyte ratio (NLR) and C-reactive protein (CRP)], and 30-day mortality. Predictors of mortality were evaluated using multivariable logistic regression and receiver operating characteristic (ROC) analysis. <b>Results</b>: A total of 234 episodes were included; <i>A. baumannii</i> accounted for 87.6% (205/234). Carbapenem non-susceptibility among <i>Acinetobacter</i> spp. isolates was 89.3% (209/234). Empiric antibiotics were initiated within 24 h in 95.7% of patients (224/234), yet only 49.6% (116/234) received at least one empiric agent later confirmed to be active. TTAT was 6 days (IQR 4-7), and active therapy within 72 h occurred in 8.5% (20/234). Thirty-day mortality was 73.1% (171/234) and did not differ between carbapenem non-susceptible (EUCAST I + R) and carbapenem-susceptible (EUCAST S) <i>A. baumannii</i> episodes (73.2% vs. 72.0%, <i>p</i> = 1.00). In multivariable analysis, age was independently associated with mortality (OR 1.36 per 10-year increase, 95% CI 1.04-1.90), with acceptable model discrimination (area under the curve = 0.74). Early NLR and CRP did not differ between carbapenem non-susceptible and carbapenem-susceptible <i>A. baumannii</i> episodes. <b>Conclusions</b>: In this ICU cohort, <i>A. baumannii</i> was the predominant species, and carbapenem non-susceptibility was highly prevalent. Despite early empiric therapy, receipt of at least one in vitro active agent was often delayed, and early inflammatory biomarkers had limited discriminatory value. These findings support locally tailored empiric strategies informed by local epidemiology and reinforce the need for improved diagnostics and stewardship interventions in high-burden ICU settings.