Abstract
Introduction: High-level aminoglycoside resistance due to 16S rRNA methylases genes have been reported in several countries. The purpose of this study was to investigate the diversity of the genes encoding 16S rRNA methylase and their associations with resistance phenotypes in Enterobacteriacae isolates.
Methods: Based on sampling size formula, from February to August 2014, a total of 307 clinical Enterobacteriaceae were collected from five hospitals in Northwest of Iran. The disk diffusion method for amikacin, gentamicin, tobramycin, kanamycin and streptomycin, as well as the MIC for aminoglycosides (except streptomycin) was used. Six 16S rRNA methylase genes (armA, npmA and rmtA-D) were screened by the PCR and sequencing assays.
Results: In the present study, 220 (71.7%) of 307 isolates were aminoglycoside-resistant and 40 isolates (18.2%, 40/220) were positive for methylase genes. The frequency of armA, rmtC, npmA, rmtB and rmtA genes were 9.5%, 4.5%, 3.6%, 2.3% and 1%, respectively. The rmtD gene was not detected in the tested bacteria. Sixty percent of positive methylase gene isolates displayed high-level resistance (MIC ≥512 µg /mL) to amikacin, kanamycin and (MIC ≥128 µg /mL) to gentamicin and/or tobramycin.
Conclusions: The prevalence of resistance to aminoglycoside in Iran is high. Furthermore, there is a statistically significant association between amikacin and kanamycin resistance with the presence of rmtC and rmtB genes.