A Single Clone of Acinetobacter baumannii, ST22, Is Responsible for High Antimicrobial Resistance Rates of Acinetobacter Spp. Isolates That Cause Bacteremia and Urinary Tract Infections in Korea

We investigated the characteristics of a total of 96 Acinetobacter spp. isolates that were shown to cause bacteremia and urinary tract infections (UTIs) from 10 university hospitals located in various regions of Korea from November 2006 to August 2007. The antimicrobial susceptibilities of these isolates were determined using a broth microdilution method, and the species were identified using molecular identification. In addition, we performed multilocus sequence typing for Acinetobacter baumannii subgroup A isolates. A. baumannii subgroup A was the most prevalent in patients with both bacteremia (32 isolates, 53.3%) and UTIs (20 isolates, 55.6%), followed by Acinetobacter genomic species 13TU (15.0% and 27.8% in bacteremia and UTIs, respectively). A. baumannii subgroup B and Acinetobacter junii were found exclusively in isolates causing bacteremia (seven and five isolates, respectively). Among 96 Acinetobacter spp. isolates, 19.8% were resistant to imipenem and 25.0% were resistant to meropenem. Most carbapenem-resistant A. baumannii isolates contained PER or oxacillinase-23-like enzymes (65.2% and 78.3%, respectively). In addition, 13.5% were resistant to polymyxin B and 17.7% were resistant to colistin. A. baumannii subgroup A isolates (52 isolates, 54.2%) showed higher resistance rates to most antimicrobial agents than other species, but not to colistin. Among A. baumannii subgroup A isolates, ST22 was the most prevalent genotype (33 isolates, 63.5%) and showed higher resistance rates to all antimicrobial agents than the other genotypes. In addition, four out of five polymyxin-resistant A. baumannii group A isolates belonged to ST22. Thus, dissemination of the main clone of A. baumannii, ST22, may contribute to the high resistance rates of Acinetobacter isolates to antimicrobials, including carbapenems, in Korea.