Objective: Aminoglycosides are an important class of antibiotics currently used for the treatment of infections caused by both gram-positive and gram-negative bacteria. Increased microbial resistance to aminoglycosides, and to the other antimicrobials is a serious problem. Plasmid-mediated 16S rRNA methylases which lead to the development of higher level resistance to aminoglycosides, involve different aminoglycoside resistance mechanisms. The aim of this study was to investigate aminoglycoside resistance caused by plasmid-mediated 16S rRNA methylases among clinical isolates of gram-negative bacteria.

Materials and Methods: Fifty-nine aminoglycoside resistant gram- negative bacteria isolated from the clinical samples at the Bacteriology Laboratory of Ege University Faculty of Medicine Department of Medical Microbiology, were included in the study. Amikacin resistance was determined by the disc diffusion method. Amikacin minimum inhibitory concentration (MIC) values for the isolates were determined by the microdilution method. The 16S rRNA methylase genes were investigated by a conventional PCR method in isolates that had high amikacin MIC values (MIC≥128 mg/L).

Results: High amikacin MIC values were found in 37 isolates. However, the genes (ArmA, rmtA, rmtB) most frequently related to the high level aminoglycoside resistance were not detected in these isolates.

Conclusion: It was concluded that the aminoglycoside resistance in these gram negative organisms was either due to the presence of different methylase genes or other resistance mechanisms. The similar studies which will be carried out in our country will be of great importance on behalf of monitorization of aminoglycoside resistance caused by methyltransferases and prevention of spread of the genes encoding these enzymes.