Aminoglycosides are potent bactericidal antibiotics targeting the bacterial ribosome, where they bind to the A-site and disrupt protein synthesis. They are particularly active against aerobic, Gram-negative bacteria and act synergistically against certain Gram-positive organisms [1–3]. Unfortunately, their efficacy has been reduced by the surge and dissemination of resistance. In some cases the levels of resistance reached the point that rendered them virtually useless . There are several considerable mechanisms that cause resistance to aminoglycosides including: 1) the acquisition of modifying enzymes such as acetyltransferases, phosphotransferases and adenylyltransferases, 2) modification of the target by mutation in ribosomal proteins  or in 16S rRNA , or by 16S rRNA methyltransferase such as ArmA , Rmt families [8, 9] and NpmA , 3) decreased intracellular accumulation of the antibiotic by alteration of outer membrane permeability, diminished inner membrane transport, or active efflux pump . The main factors contributing to the increasing isolates resistant to aminoglycosides were reported to be the widespread genes encoding aminoglycoside-modifying enzymes and 16S rRNA methyltransferase [2, 12–14]. The most common aminoglycoside-modifying enzyme gene types are aac(3)-II, followed by aac(6′)-I, ant(3″)-I, aph(3′)-II, and ant(2″)-I in Escherichia coli. Furthermore, aac(6′)-II and aph(3′)-VI are respectively the significant resistance determinants of gentamicin, tobramycin, and amikacin in Pseudomonas aeruginosa[4, 16]. In addition, modification of 16S rRNA by methylases reduces binding to aminoglycosides, leading to high-level resistance to amikacin, kanamycin, tobramycin and gentamicin . Currently, seven 16S rRNA methylase genes have been identified (armA, rmtA, rmtB, rmtC, rmtD, rmtE, rmtF and npmA), among which, armA and rmtB are the most common 16S rRNA methyltransferase genes [9, 14, 18, 19].
Characterization and distribution of antimicrobial resistance gene profiles provide important information on the potential difficulty of treatment of bacteria. This information can be used to facilitate prompt and effective treatment of bacterial infections. In order to investigate the prevalence of aminoglycoside-resistance genes, several methods have been developed, including conventional single PCR and multiplex PCR assays combined with agarose gel electrophoresis analysis, hybridization with DNA probes, and sequence analysis [20, 21]. Some drawbacks with these existing methods are time-consuming, labor-intensive, and difficult to analyze multiple genes simultaneously. DNA chips provide a versatile platform for rapidly screening several thousand potential antimicrobial resistance genes in parallel [22, 23]. However, it is expensive and time-consuming for detecting numerous clinical isolates in the epidemiological investigation. So it is necessary to develop a rapid, cost effective and high throughput method to investigate the distribution of aminoglycoside resistance gene in clinical isolates.
The GenomeLab Gene eXpression Profiler genetic analysis system (GeXP analyzer) provided by Beckman Coulter Company (Brea, CA, USA) has been adopted by our group and successfully applied in the rapid detection of pandemic influenza A H1N1 virus , simultaneous detection of 11 human papillomavirus (HPV) genotypes , sixteen human respiratory virus types/subtypes  and nine serotypes of enteroviruses associated with hand, foot, and mouth disease  with high sensitivity and specificity. The general analysis procedure of GeXP assay consists of chimeric primer-based multiplex PCR amplification and capillary electrophoresis separation. In this study, a high throughput, cost-effective GeXP analyzer-based multiplex PCR assay (GeXP assay) was developed to simultaneously detect seven aminoglycoside- resistance genes, including five aminoglycoside-modifying enzymes genes [aac(3)-II, aac(6′)-Ib, aac(6′)-II, ant(3″)-I and aph(3′)-VI] and two 16S rRNA methyltransferase genes [armA and rmtB], and the results were compared with that of the conventional single PCR assay.