Distribution and Antimicrobial Resistance Patterns of Critical and High-Priority Gram-Negative Pathogens Isolated from Endotracheal Aspirates in an Intensive Care Unit

Lower respiratory tract infections represent the world’s deadliest infectious disease, responsible for approximately 2.5 million deaths worldwide. The aim of the study was to determine the distribution and antimicrobial susceptibility profiles of the main critical and high priority Gram-negative bacteria isolated from endotracheal aspirates obtained from Intensive Care Unit (ICU) patients. We conducted a four-year microbiological surveillance study (2022–2025) in a tertiary Romanian ICU. A total of 1529 Gram-negative bacterial isolates were detected in 1391 endotracheal aspirates. Most frequently reported were Pseudomonas aeruginosa (422–27.60%), Acinetobacter baumannii (296–19.36%), Escherichia coli (274–17.92%) and Klebsiella pneumoniae (271–17.73%). The prevalence of MDR Acinetobacter baumannii declined to approximately 40% in 2025, whereas XDR isolates increased to 13.51%, twice the 2022 value. Carbapenem resistance among Acinetobacter baumannii remained high (around 70%) in 2025, despite a significant decline from 2022 (p < 0.001). Approximately 65% of K. pneumoniae isolates were MDR/XDR, with an increase in carbapenem resistance. MDR Pseudomonas aeruginosa increased significantly from 14.14% in 2022 to 39.84% in 2025 (p < 0.001) and a significant upward trend in carbapenem resistance was registered, exceeding 70% for imipenem in 2025. These findings underscore the need for continuous microbiological and epidemiological surveillance and targeted interventions to prevent the spread of highly resistant pathogens.