The aim of our study was to investigate mechanisms of aminoglycoside resistance in extended-spectrum beta-lactamases (ESBL)-producing Klebsiella pneumoniae (K. pneumoniae) isolates from Iran. To this end, 154 clinical isolates of K. pneumoniae were collectedfrom two hospitals in Ilam city, Iran. The Kirby-Bauer (agar diffusion) antibiotic testing method was used to determine the susceptibilitypattern of the isolates against kanamycin, gentamicin, tobramycin, netilmicin and amikacin. Aminoglycoside acetyltransferases(aac(3)-IIa, aac(6’)-Ib, and aac(3)-Ia), 16SrRNA methylase genes (armA and rmtB) and ESBL genes (blaTEM, blaSHV , and blaCTX-M)were detected by PCR amplification. 59.1% (n = 91) of K. pneumoniae isolates were detected ESBL producers with the phenotypic test.Moreover, blaTEM, blaSHV and blaCTX-M were detected in 83.5% (n=76), 52.7% (n=48) and 26.4% (n=24) of the ESBL-producing isolates,respectively. Among 52 resistant or intermediate isolates against aminoglycosides, the aac(3)-IIa, aac(6’)-Ib and rmtB genes were detectedin 55.8% (n = 29), 80.8% (n = 42) and 1.9% (n = 1) of the isolates, respectively; none of the isolates, however, had the aac(3)-Iaand armA genes. Therefore, the results showed the high prevalence of aminoglycosides resistance in the K. pneumoniae isolates. Asobserved, the acetyltransferase modifying enzymes (aac genes) played major roles in determining this resistance. However, the rateof 16srRNA methylase genes was extremely low in K. pneumoniae.
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