The Major Aminoglycoside-Modifying Enzyme AAC(3)-II Found inEscherichia coliDetermines a Significant Disparity in Its Resistance to Gentamicin and Amikacin in China

Abstract

The aim of this study was to investigate the prevalence of aminoglycoside-modifying enzymes in Escherichia coli in different areas of China and to explore the relationship between pandemic enzyme type and bacterial resistance to antimicrobial agents in China. Gentamicin- or etimicin-resistant clinical isolates of E. coli were collected from different areas of China, and the in vitro antibacterial activity of 11 aminoglycoside agents was determined using standard (Clinical and Laboratory Standards Institute) agar dilution methods. Twelve aminoglycoside-modifying enzyme genes were detected by PCR and confirmed by DNA sequencing. A total of 205 E. coli strains were collected from nine hospitals in seven cities. All strains were highly resistant to gentamicin or etimicin, whereas resistance to tobramycin, netilmicin, and kanamycin was slightly lower. However, less than 15% of isolates were resistant to amikacin and isepamicin. Of the gentamicin-resistant strains, 88.2% and 86.7% were sensitive to isepamicin and amikacin, respectively. Five aminoglycoside-modifying enzyme genes were detected in 191 strains, whereas the remaining 14 strains were negative. The most common gene type was aac(3)-II (162 strains), followed by aac(6')-I (50 strains), ant(3″)-I (28 strains), aph(3')-II (20 strains), and ant(2″)-I (20 strains). Ninety-five strains yielded aac(3)-II only, whereas the others contained two or three genes. The three main gene combinations were aac(6')-I/aac(3)-II (28 strains), aac(3)-II/ant(3″)-I (11 strains), and aac(3)-II/aac(6')-I (10 strains). Regional bacterial resistance and enzyme distribution were roughly similar, although minor differences were found in Guangzhou, Jinan, and Dalian, which were the sources of most of the amikacin- or isepamicin-resistant strains. Chinese clinical isolates of E. coli remain highly resistant to gentamicin and etimicin, but are susceptible to amikacin and isepamicin. The dominant type of aminoglycoside-modifying enzyme, AAC(3)-II, might be the main source of the disparity in E. coli resistance to different aminoglycoside agents.