The Impact of the COVID-19 Pandemic on the Antibiotic Resistance of Gram-Negative Pathogens Causing Bloodstream Infections in an Intensive Care Unit

<b>Background/Objectives</b>: In this research, we aimed to analyze the trend of the antimicrobial resistance pattern of Gram-negative isolated in blood samples collected from patients with severe invasive infections hospitalized in the intensive care unit in selected periods during and after COVID-19. <b>Methods</b>: A retrospective study of bacterial pathogens was performed on 481 patients admitted to the ICU between 2020 and 2023. The resistance patterns were analyzed using the Vitek 2 Compact system. <b>Results</b>. A total of 686 Gram-negative bacterial isolates were obtained. The most frequently detected Gram-negative pathogens were <i>Klebsiella</i> spp. (30.91%), <i>Acinetobacter</i> spp. (24.64%), and <i>Escherichia coli</i> (18.95%). Almost 50% of all the pathogens were multidrug-resistant, with a statistically significant increase post-pandemic (<i>p</i> < 0.05). Post-pandemic, the study highlighted a significantly higher percentage of the <i>Klebsiella</i> strains (<i>p</i> < 0.05), and a significant increase in the antibiotic resistance rate against colistin (<i>p</i> < 0.001) and tigecycline (<i>p</i> = 0.005). A very high percentage of MDR Acinetobacter spp. isolates was found, with a significant increase in the antibiotic resistance rate against colistin (<i>p</i> < 0.001). A significantly lower resistance was recorded for the <i>Escherichia coli</i> strains in the case of ceftazidime (<i>p</i> = 0.03) and aminoglycosides (gentamicin-<i>p</i> = 0.01, amikacin-<i>p</i> < 0.001). An increase in the percentage of carbapenem-resistant <i>Klebsiella</i> spp., <i>Acinetobacter</i> spp., and <i>Enterobacter</i> spp. strains was observed, and a significant decrease in the in the case of <i>Proteus</i> spp. (<i>p</i> = 0.01). <b>Conclusions</b>: Our findings revealed a statistically significant increase in the resistance rate to last-line antibiotics and in the percentage of MDR Gram-negative strains isolated in the blood samples in the post-COVID-19 era.