“In vitro evaluation of sulbactam combination therapies for Acinetobacter baumannii”

ABSTRACT Background and objectives Acinetobacter baumannii , a leading cause of hospital-acquired infections in critically ill patients, is increasingly resistant to carbapenems, leading WHO to designate carbapenem-resistant Acinetobacter baumannii (CRAB) as a critical priority pathogen. While the 2024 IDSA guidelines recommend sulbactam-based regimens as the cornerstone of therapy, high-dose sulbactam is effective only against isolates with MICs up to 16–32 μg/mL. This study aimed to describe the sulbactam MIC distribution and to evaluate MIC reduction and synergy when combined with β-lactam antibiotics against CRAB. Methods CRAB isolates from respiratory samples of ventilator-associated pneumonia patients were tested using E-tests to determine MICs of individual antibiotics. Combinations of sulbactam with ceftriaxone, cefepime, and meropenem were assessed using the E-test cross method. Synergy was evaluated by the FIC index: synergy (≤0.5), additive (>0.5–1), indifference (>1–