Distribution of aminoglycoside-modifying enzyme genes in Escherichia coli isolated from urinary tract infections

Urinary tract infections (UTIs) are among the most common bacterial infections worldwide. Escherichia coli is responsible for more than 80% of community- and hospital-acquired UTIs. Aminoglycosides are widely used as first-line therapy for severe Gram-negative infections, but antimicrobial resistance particularly through aminoglycoside-modifying enzymes (AMEs) threatens treatment success. The aim of this study was to investigate the relationship between aminoglycoside resistance and the prevalence of genes encoding modifying enzymes in Escherichia coli isolates obtained from urinary tract infections. This cross-sectional study was performed at Babol University of Medical Science. A total of 178 E. coli isolates were collected from urine samples of UTI patients. Antimicrobial susceptibility testing was performed according to CLSI guidelines, and the presence of AME-encoding resistance genes (aac(6')-Ib-cr, aadA1, aphA1, aph(6), Aph(6'-VI) was examined using PCR. Overall, 71% of isolates were from females and 29% from males; 57% were obtained from children and 43% from adults. Phenotypic results showed high susceptibility to gentamicin (78%) and amikacin (75%), while resistance was 20.8% and 18%, respectively. The most frequent AME gene was aac(6')-Ib-cr (37%), followed by aphA1 (15%) and aadA1 (14%). Statistical analysis showed a significant association only between aphA1 and gentamicin resistance. Although aminoglycoside susceptibility remains high, AME genes are already disseminating among uropathogenic E. coli, indicating the risk of future resistance expansion. Phenotypic and genetic data provide valuable guidance for treatment and resistance monitoring.