Changes in antimicrobial susceptibility and major clones of Acinetobacter calcoaceticus-baumannii complex isolates from a single hospital in Korea over 7 years.

Acinetobacter spp. has emerged as an opportunistic nosocomial pathogen in intensive care units. Epidemic spread and outbreaks of multidrug-resistant or carbapenem-resistant Acinetobacter baumannii infections have been described worldwide. For Acinetobacter spp. isolates collected from a single institution in Korea over 7-years, species distribution, antimicrobial resistances, and genotypes were investigated. Two hundred eighty-seven Acinetobacter spp. isolates were collected from patients with bloodstream infections in one Korean hospital during the 7 years from 2003-2010. Most of them belonged to A. calcoaceticus-baumannii (Acb) complex (94.4%). The most frequently isolated species was A. baumannii (44.2%), followed by A. nosocomalis (formerly Acinetobacter genomic species 13TU) (34.1%). The proportion of A. baumannii increased significantly from 2008-2010 (40.4% to 50.0%). Since 2008, imipenem and meropenem resistance rates increased significantly compared with 2003-2007 (12.9% and 20.5%, respectively, to 41.4% and 41.5%, respectively). An increased carbapenem resistance rate between the two periods was identified more clearly among A. baumannii isolates. Polymyxin-resistant A. baumannii isolates emerged in 2008-2010, despite the availability of few isolates. The increase of carbapenem resistance in A. baumannii might be due to the substitution of main clones. Although ST92 and ST69 were the most prevalent clones among A. baumannii in 2003-2007 (47.8% and 15.9%, respectively), ST75 and ST138 had increased in 2008-2010 (39.7% and 25.9%, respectively). Although ST92 showed moderate resistance to carbapenems, most ST75 and ST138 isolates were resistant to carbapenems. All ST75 and ST138 isolates, but only one ST92 isolate, contained the blaOXA-23-like gene. Increased carbapenem resistance in Acinetobacter spp. and A. baumannii isolates might be due to the expansion of specific carbapenem-resistant clones.