Abstract:

Objective To study the drug resistance of extended-spectrum beta-lactamases（ESBLs）-producing Escherichia coli to aminoglycosides and the expression frequencies and sequences of drug resistant genes in Jiangchuan District,Yuxi City,Yunnan Province. Methods The drug resistance of 32 isolates of ESBLs-producing Escherichia coli to gentamycin,amikacin,kanamycin,tobramycin and netilmicin was determined by disk diffusion test. A total of 7 aminoglycoside-modifying enzyme（AME） genes [aac（3）-Ⅰ,aac（3）-Ⅱ,aac（6′）-Ⅰad,aac（6′）-Ⅰb,aac（6′）-Ⅱ,ant（3″）-Ⅰ and ant（2″）-Ⅰ] and 6 genes of 16S rRNA methylases（armA,rmtA,rmtB,rmtC,rmtD and npmA） were determined by polymerase chain reaction（PCR）,and the sequence of aac（3）-Ⅱ gene was analyzed by double deoxidizing terminal cessation method. Results The drug resistant rates of 32 isolates of ESBLs-producing Escherichia coli to gentamycin,amikacin,netilmicin,kanamycin and tobramycin were 100%,0%,0%,18% and 87%,respectively. It was found that 2 AME genes existed simultaneously in 6 isolates. The positive rates of 4 AME genes,aac（3）-Ⅱ,aac（6′）-Ⅰb,ant（3″）-Ⅰ and ant（2″）-Ⅰ,were 100%,9.4%,6.2% and 3.1% in 32 isolates. There was no gene of 16S rRNA methylases. The aac（3）-Ⅱ mutations existed in 4 out of 32 isolates,which were G232A,T251C,G580A and T612A,respectively. There was no gene of AME and 16S rRNA methylases in 8 isolates of ESBLs-producing Escherichia coli. Conclusions The drug resistance of ESBLs-producingEscherichia coli to aminoglycosides was correlated with AME gene expressions,and the mutations of aac（3）-Ⅱ may contribute to the increased drug resistance to netilmicin.

Key words: Escherichia coli, Aminoglycoside-modifying enzyme genes, 16S rRNA methylase gene