Pediatric Urinary Antimicrobial Resistance Patterns in a Tertiary Hospital of Northern Greece: A Retrospective Laboratory-Based Surveillance Study

Background/Objectives: Antimicrobial resistance in pediatric urinary tract infections (UTIs) is a growing concern. We evaluated resistance patterns of Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa urinary isolates in a tertiary care Greek hospital from 2015 through 12 September 2025. Methods: We retrospectively analyzed pediatric urinary isolates collected from 2015 through September 2025. Antibiotic analysis was restricted to EUCAST UTI-relevant organism-drug pairs. Resistance was summarized for the prespecified antibiotics, and presumptive ESBL and carbapenem resistance phenotypes were assessed. Results: Among 776 isolates (567 E. coli, 104 K. pneumoniae, 105 P. aeruginosa), E. coli showed the lowest resistance among non-carbapenem options to nitrofurantoin (0.4%), amikacin (1.2%), and gentamicin (7.8%), and the highest to trimethoprim (98.8%), ampicillin (53.5%), and trimethoprim-sulfamethoxazole (31.5%). K. pneumoniae had the lowest resistance among non-carbapenem options to amikacin (8.6%) and gentamicin (15.5%), with high cephalosporin resistance (oral cefuroxime 40.9%, intravenous cefuroxime 39.7%). Presumptive ESBL and carbapenem resistance in K. pneumoniae were 42.3% and 20.2%, respectively. Corresponding prevalences in E. coli were 12.4% and 0.7%. P. aeruginosa retained low resistance to meropenem (1.9%) and piperacillin-tazobactam (2.1%). No age or sex association with the presumptive resistance phenotypes remained significant after false-discovery-rate adjustment. Conclusions: E. coli showed very high ampicillin resistance, low resistance to gentamicin and amikacin, and moderate resistance to guideline-relevant cephalosporins. P. aeruginosa retained low resistance to key antipseudomonal agents. K. pneumoniae showed the highest burden of cephalosporin resistance and of presumptive ESBL and carbapenem resistance phenotypes. These data support guideline-based empirical coverage more strongly for E. coli than for K. pneumoniae in this setting.