Antimicrobial Resistance Trends in Acinetobacter spp. and Pseudomonas spp. Across the Pre-, Pandemic, and Post-COVID-19 Periods

Introduction: The Coronavirus Disease-2019 (COVID-19) pandemic substantially changed healthcare delivery and may have influenced antimicrobial resistance (AMR) through increased empirical antibiotic prescribing, prolonged intensive care admissions, and extensive use of invasive interventions.As leading causes of healthcare-associated bloodstream infections, Acinetobacter spp.and Pseudomonas spp.represent important indicators for evaluating changes in resistance patterns over time.This study investigated temporal variations in AMR among these pathogens before, during, and after the COVID-19 pandemic.Methods: A retrospective observational study was conducted at University of Health Sciences Türkiye, İstanbul Haseki Training and Research Hospital using blood culture isolates collected from January 2017 to December 2023.Adult hospitalized patients with nonfermentative Gram-negative bloodstream isolates were included.Antimicrobial susceptibility testing was interpreted according to the European Committee on Antimicrobial Susceptibility Testing breakpoints applicable at the time of analysis, and resistance profiles were compared across the pre-pandemic, pandemic, and post-pandemic periods.Results: Overall, 740 Acinetobacter spp.and 268 Pseudomonas spp.isolates were evaluated.Acinetobacter spp.demonstrated a progressive increase in resistance to meropenem, colistin, gentamicin, and amikacin, with the highest resistance rates observed after the pandemic (all p<0.001).Meropenem resistance reached 98%, whereas colistin resistance increased to 32.2%.In contrast, Pseudomonas spp.exhibited significantly lower resistance to amikacin, gentamicin, ciprofloxacin, and imipenem during the postpandemic period (all p<0.05), although the proportion of isolates with intermediate susceptibility increased for several antimicrobial agents.Conclusion: Distinct changes in AMR patterns were observed following the COVID-19 pandemic, and these changes differed between bacterial species.The substantial increase in resistance among Acinetobacter spp., compared with the relatively favorable susceptibility profile of Pseudomonas spp., reinforces the need for ongoing local resistance surveillance, effective antimicrobial stewardship programs, and strengthened infection prevention measures.