Multidrug-Resistant Acinetobacter baumannii: Resistance Mechanisms, Emerging Therapies, and Prevention—A Narrative Review

<i>Acinetobacter baumannii</i> is a leading intensive care unit (ICU) pathogen associated with high rates of carbapenem resistance and poor clinical outcomes. This narrative review synthesizes recent clinical, microbiological, and pharmacokinetic/pharmacodynamic (PK/PD) evidence regarding resistance mechanisms and therapeutic strategies. A literature review was performed in PubMed, Scopus, and Web of Science (January 2015-August 2025), focusing on multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains, ICU-acquired infections, and pivotal trials involving cefiderocol and sulbactam-durlobactam. Resistance is driven by OXA-type carbapenemases (notably OXA-23/24/58), efflux systems (AdeABC/IJK/FGH), porin alterations (CarO, Omp33-36), and lipopolysaccharide (LPS) modifications conferring colistin resistance. Management options include polymyxins, optimized tigecycline dosing, β-lactam/β-lactamase inhibitors, and newer agents such as cefiderocol and sulbactam-durlobactam, though mortality and safety outcomes vary across trials. A comparative table is included, summarizing antimicrobial mechanism coverage, PK/PD parameters, and adverse effects to support regimen selection in ventilator-associated pneumonia (VAP) and bacteremia. Optimized, multimodal approaches integrating timely diagnostics, targeted combination therapies, infection prevention, and antimicrobial stewardship are essential to improve outcomes and limit the spread of MDR and XDR <i>A. baumannii</i>.