Trends in the Frequency and Antimicrobial Resistance of Common Gram-Negative Bacilli Isolated From Urine Cultures

The sustained increase in antimicrobial resistance among Gram-negative bacilli (GNB) compromises the effectiveness of empirical treatment regimens. This study aims to describe the evolution of the frequency and antimicrobial resistance profiles of the most commonly isolated GNB in urine cultures in our area. A cross-sectional, descriptive, and retrospective study was conducted, analyzing urine cultures from patients with suspected UTIs between 2021 and 2025. Microorganism identification was performed using MALDI Biotyper or MicroScan systems, and antimicrobial susceptibility testing was carried out using MicroScan, interpreted according to EUCAST guidelines. A total of 81,791 urine cultures were analyzed. In E. coli, a significant increase in resistance was observed for amoxicillin-clavulanate, ciprofloxacin, piperacillin-tazobactam, and fosfomycin (from 3.48% in 2021 to 25.31% in 2025). Klebsiella pneumoniae showed a marked increase in resistance to fosfomycin (from 27.25% to 79.73%) and imipenem. Pseudomonas aeruginosa, predominantly hospital-acquired, exhibited a significant increase in resistance to piperacillin-tazobactam, imipenem, and antipseudomonal cephalosporins. The evolution of antimicrobial resistance in uropathogenic GNB in our region is complex and dynamic. The spread of carbapenemases highlights the need for rigorous local epidemiological surveillance and optimization of antimicrobial stewardship programs to guide empirical therapy and infection control measures.