Differences in phenotypic and genotypic traits against antimicrobial agents between Acinetobacter baumannii and Acinetobacter genomic species 13TU

Objectives: To investigate the differences in antimicrobial susceptibility and resistance mechanisms against imipenem between Acinetobacter baumannii and Acinetobacter genomic species 13TU. Methods: A total of 232 non-duplicate Acinetobacter species were consecutively collected from two Korean hospitals in Daegu, Republic of Korea, between November 2004 and November 2005. Antimicrobial susceptibility was determined by agar dilution methods. Resistance to imipenem was characterized by a carbapenemase activity test and PCR amplification. PFGE was performed to determine the clonal relatedness of imipenem-resistant Acinetobacter species. Results: A. baumannii was the most prevalent species (61.2%), followed by Acinetobacter genomic species 13TU (25.9%). The resistance rates of A. baumannii to most antimicrobial agents were higher than those of other Acinetobacter species, while the resistance rate to imipenem was the highest in Acinetobacter genomic species 13TU. Imipenem-resistant Acinetobacter genomic species 13TU isolates produced VIM-2 metallo-beta-lactamase, while imipenem-resistant A. baumannii isolates produced OXA-23 and/or OXA-51 p-lactamase. lmipenem-resistant Acinetobacter strains originated from different clones in each hospital. Conclusions: Two prevalent Acinetobacter species, A. baumannii and Acinetobacter genomic species 13TU, possess distinct phenotypic and genotypic traits against antimicrobials.