Trends in antimicrobial resistance of major gram-negative uropathogens, 2016–2024: A single center retrospective study

Purpose: Resistance to empiric antimicrobials has become markedly higher among gram-negative uropathogens in Korea, compared to those in Europe and North America.To guide empiric treatment strategies and to build real evidence, we conducted a retrospective analysis of antimicrobial susceptibility patterns from urine cultures obtained at a university hospital.Materials and Methods: Antimicrobial susceptibility test (AST) results from initial positive urine cultures (n=11,358, both inpatients and outpatients) collected between 2016 and 2024 were reviewed.The analysis focused on predominant gram-negative isolates-Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Pseudomonas aeruginosa.Resistance rates were determined for twelve commonly used antimicrobials, including third-and fourth-generation cephalosporins, β-lactam/β-lactamase inhibitor combinations, carbapenems, aminoglycosides, fluoroquinolones, trimethoprim/sulfamethoxazole, nitrofurantoin, and fosfomycin.Results: Between 2016 and 2024, AST identified E. coli (n=6,533), K. pneumoniae (n=1,348), P. mirabilis (n=677), and P. aeruginosa (n=663).While fluoroquinolone resistance remained persistently high (31.5%-44.5% in E. coli, 6.9%-37.0% in K. pneumoniae), its annual trend showed to be stable.Cefepime resistance increased steadily in most gram-negative isolates (annual percentage change [APC]=16.1%-25.0%).Although Carbapenem resistance remained low but it increased steadily in E. coli and K. pneumoniae (APC=22.2%).Nitrofurantoin and fosfomycin retained strong activity against E. coli, though their efficacy varied among other pathogens.Conclusions: This 9-year longitudinal study reveals sharp cefepime resistance increases post-2019 and persistently high fluoroquinolone resistance among major four gram-negative uropathogens.Targeted antimicrobial stewardship are essential to optimize urinary tract infection management and reduce unnecessary broad spectrum antimicrobials in Korea.