Genetic basis of resistance to aminoglycosides in Acinetobacter spp. and spread of armA in Acinetobacter baumannii sequence group 1 in Korean hospitals

A total of 75 Acinetobacter isolates resistant to all available aminoglycosides obtained from 2 Korean hospitals were studied for the genctic basis of resistance to aminoglycosides. The MIC50 and MIC90 of Acinetobacter baumannii isolates (n = 61) to amikaein, gentamicin. isepamycin spectinomycin, streptomycin, and tobramycin were higher than those of Acinetobacter genomic species 13TU isolates (n = 14). Genes encoding aminoglycoside-modifying enzymes, ant(3 '')-Ia, aac(6')-Ib, aph(3')-Ia, aac(3)-Ia, and aph(3')-VI, and 16S ribosomal RNA (rRNA) methylase armA were detected. ant(3 '')-Ia and aac(6')-Ib were commonly detected in both Acinetobacter spp., but armA and aph(3 ''')-Ia were only detected in A. baumannii. armA was located on the plasmids. A. baumannii isolates carrying armA were classified into 7 pulsotypes but belonged to sequence group 1. The combination of aminoglycoside-modifying enzymes is responsible for the moderate-level resistance to aminoglycosides in Acinetobacter genomic species 13TU, whereas armA is responsible for the high-level resistance to aminoglycosides in A. baumannii sequence group 1. (C) 2009 Elsevier Inc. All rights reserved.