Prevalence and antimicrobial resistance of Acinetobacter baumannii isolated from endotracheal aspirates in a tertiary-care intensive care unit from South India

Abstract

Background – Multidrug-resistant (MDR) Acinetobacter baumannii is a major cause of ventilator-associated infections in intensive care units (ICUs), where empirical therapy is often initiated without up-to-date antimicrobial resistance (AMR) surveillance data. This study assessed the prevalence, demographic associations, and antimicrobial susceptibility patterns of MDR A. baumannii isolated from endotracheal (ET) aspirates in a tertiary-care hospital in southern India. Methods – In this single-center retrospective observational study, 3, 540 non-duplicate clinical isolates collected between 2019 and 2025 were analyzed. Bacterial identification and antimicrobial susceptibility testing were performed using the Vitek 2 Compact automated system and the Kirby–Bauer disc diffusion method, with results interpreted in accordance with Clinical and Laboratory Standards Institute (CLSI) performance standards. Receiver operating characteristic (ROC) curve analysis was used to evaluate the discriminatory performance of the commonly used antibiotics, with the results expressed as the area under curve (AUC). Results – MDR A. baumannii accounted for 20.2% of all isolates, with the highest prevalence among neurosurgical ICU patients (22.1%). Isolates were more frequent in males (74%) and in patients aged ≥30 years. Resistance was highest for carbapenems (meropenem, 66.4%; imipenem, 62.6%), ciprofloxacin (71.8%), and trimethoprim–sulfamethoxazole (53.1%). Amikacin showed the greatest relative activity and the highest AUC (0.63), but overall discriminatory performance of all tested agents was modest. Conclusion – MDR Acinetobacter baumannii is highly prevalent in intensive care units in this setting and shows extensive resistance to carbapenems, fluoroquinolones, and other commonly used agents. Although amikacin demonstrated comparatively better in vitro activity and the highest AUC, its modest discriminatory performance indicates limited reliability as monotherapy. These findings support the use of ICU-specific susceptibility data from endotracheal aspirates to guide empirical therapy and highlight the need for targeted stewardship interventions in high-burden critical care units.