Abstract:

Objective　To investigate the double-circle drug resistance gene to amikacin (AMK) in Entero-bacteriaceae by disk diffusion methodand to study the influence on the expression level of resistance gene mRNA. Methods　One strain of Escherichia coli (Eco85) and one strain of Klebsiella pneumoniae (Kpn110) which showed double-circle drug resistance to AMK were collected, and the resistance phenotype change was analyzed by disk diffusion method. Polymerase chain reaction (PCR) was performed for aminoglycoside modification genes, integronsand 16S rRNA methylase gene. The armA gene expression levels among strains induced and non-induced by AMK were studied by reverse transcription PCR. Transmissibility of the resistant gene was carried out by conjugation method. Results　The double-circle resistance phenotype was changed to complete resistance at the tenth and sixteenth for Eco85 and Kpn110, respectively. The 2 strains were positive for integron geng Ⅰ, Eco85 and Kpn110 contained aadA5-dfra17 box and aadA2-dfrA12 box, respectively. The 2 strains were positive for integron gene Ⅱ and Ⅲ. Eco85 was positive for aac(6)-Ⅰ gene, and Kpn110 was positive for ant (3″)-Ⅰ gene. Eco 85 and Kpn 110 were positive for armA gene, and there was no mutation in gene sequencing and no rmt B gene. The expression level of armA gene mRNA was significantly up-regulated when the strains were induced by AMK. The conjugation test was failed. Conclusions　The double-circle drug resistance to AMK in Escherichia coli and Klebsiella pneumoniae may associate with the induction expression of 16S rRNA methylase armA gene.

Key words: Double-circle drug resistance, Induction, armA gene, Amikacin, Enterobacteriaceae, Reverse transcription polymerase chain reaction