Molecular Characterization of Aminoglycoside-modifying Enzymes (AMEs)in Aminoglycoside-Resistant Staphylococcus aureus: A Cross-sectional Study in Northeastern Iran.

Background & objective: The resistance genes encoding aminoglycoside-modifying enzymes (AMEs) are now widely prevalent in different populations of Staphylococcus aureus. The study aimed to determine the frequency of AMEs-encoding genes in clinical isolates of S. aureus.

Methods: A total of 105 S. aureus isolates were obtained from the different clinical samples; and then were identified by conventional biochemical tests. The antibiotic resistance patterns of the isolates were characterized by the agar disk diffusion method. The distribution of the AMEs and femA genes was determined by conventional and multiplex PCR.

Results: The aminoglycoside resistance rates of kanamycin, tobramycin, gentamicin, amikacin, and netilmicin were 47.6%, 46.6%, 45.7%, 45.7%, and 26.6%, respectively. 16.1% and 1.9% of isolates were MDR and XDR phenotypes, respectively. 21.9% of S. aureus isolates harbored the femA gene and were determined as methicillin-resistant S. aureus (MRSA) clones. The aac(6')/aph(2'') was the most prevalent (47.8%) AME-encoding gene in aminoglycoside-resistant S. aureus, followed by ant(4')-Ia (30.4%) and aph(3')-IIIa (21.7%).

Conclusion: Our study demonstrated that the coexistence of several AMEs and the spread of the resistance determinants like femA in S. aureus clinical isolates are alarming and may contribute to the broadening of aminoglycoside resistance spectra and limit treatment options for staphylococcal infections.