Distribution and antibiotic resistance of Gram-negative bacteria from blood cultures before and during the COVID-19 pandemic

INTRODUCTION: Antimicrobial resistance in bloodstream infections is an important clinical challenge. The impact of the coronavirus disease 2019 (COVID-19) pandemic on antimicrobial resistance remains a subject of ongoing debate. This single-center study aimed to analyze Gram-negative bacteria (GNB) isolated from blood cultures and evaluate changes in antimicrobial resistance between the pre-pandemic (March 2018-February 2020) and pandemic (March 2020-February 2022) periods. METHODOLOGY: Blood culture data collected over 4 years were retrospectively analyzed using the BACT/ALERT 3D system. Bacterial identification was conducted with the VITEK® 2 compact system, and antimicrobial susceptibility testing was performed according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. RESULTS: Of 1,668 positive blood cultures, 38.3% yielded GNB. There was an increase in Gram-negative isolates during the pandemic, compared to the pre-pandemic period (55.9% vs. 44.1%). Resistance changes were detected in extensive antibiogram analyses in which 18 different antibiotics were studied for the 4 most frequently isolated species, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. During the pandemic period, resistance to amoxicillin/clavulanic acid, ampicillin, ampicillin-sulbactam, ceftriaxone, and cefuroxime decreased; while resistance to amikacin, levofloxacin, and cefepime increased; except in Escherichia coli. CONCLUSIONS: K. pneumoniae remained the most frequently isolated bacterium in both periods, while A. baumannii showed a significant increase during the pandemic. The 2.6-fold increase in A. baumannii may have been caused by the increased use of broad-spectrum antibiotics during the pandemic. These findings reflect data from a single hospital and should be validated by further multicenter studies.