Trends in Antimicrobial Resistance of Acinetobacter baumannii and Pseudomonas aeruginosa from Bloodstream Infections: An Eight-Year Study in a Romanian Tertiary Hospital

<b>Background</b>: Bloodstream infections (BSIs) caused by multidrug-resistant non-fermenting Gram-negative bacilli, particularly <i>Pseudomonas aeruginosa</i> and <i>Acinetobacter baumannii</i>, represent a growing public health concern, especially in tertiary care settings. This study aimed to describe the epidemiological and antimicrobial resistance trends of <i>P. aeruginosa</i> and <i>A. baumannii</i> isolated from blood cultures over an eight-year period (2017-2024) at a tertiary infectious disease hospital in Bucharest, Romania, especially in the context of the disruption caused by the SARS-CoV-2 pandemic. <b>Methods</b>: A retrospective study was conducted on 43,951 blood cultures processed at the National Institute of Infectious Diseases. Species identification and antibiotic susceptibility testing (AST) were performed using VITEK2, MALDI-TOF MS, and supplementary phenotypic methods. AST interpretation followed EUCAST guidelines. <b>Results</b>: Out of all of the positive blood cultures, 112 (3.63%) were <i>P. aeruginosa</i> and 158 (5.12%) <i>A. baumannii</i>. Multidrug-resistance (MDR) was identified in 46% of <i>P. aeruginosa</i> and 90.73% of <i>A. baumannii</i> isolates. Resistance trends varied, with <i>P. aeruginosa</i> showing a decrease in MDR rates post-COVID-19 pandemic and following antimicrobial stewardship implementation. In contrast, <i>A. baumannii</i> displayed persistently high resistance, with carbapenem and aminoglycoside resistance rates reaching 100% by 2024. Colistin resistance, though low overall, increased in the latter years. <b>Conclusions</b>: The findings highlight the dynamic nature of antimicrobial resistance among <i>P. aeruginosa</i> and <i>A. baumannii</i>. Effective infection control and antimicrobial stewardship programs are crucial in curbing the rise of MDR strains, particularly amid healthcare system disruptions such as the COVID-19 pandemic.