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Journal of Clinical Microbiology, June 2008, p. 2052-2059, Vol. 46, No. 6
0095-1137/08/$08.00+0     doi:10.1128/JCM.00014-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Oligonucleotide Array-Based Identification of Species in the Acinetobacter calcoaceticus-A. baumannii Complex in Isolates from Blood Cultures and Antimicrobial Susceptibility Testing of the Isolates

Departments of Internal Medicine,¹ Pathology,² Center of Infection Control, National Cheng Kung University Hospital,³ Departments of Medicine,⁴ Medical Laboratory Science and Biotechnology, Medical College, National Cheng Kung University, Tainan, Taiwan,⁵ Department of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands,⁶ Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University Hospital, Ghent, Belgium⁷

Received 4 January 2008/ Returned for modification 10 March 2008/ Accepted 21 March 2008

Acinetobacter calcoaceticus, A. baumannii, Acinetobacter genomic species (gen. sp.) 3, and Acinetobacter gen. sp. 13TU, which are included in the A. calcoaceticus-A. baumannii complex, are difficult to distinguish by phenotypic methods. An array with six oligonucleotide probes based on the 16S-23S rRNA gene intergenic spacer (ITS) region was developed to differentiate species in the A. calcoaceticus-A. baumannii complex. Validation of the array with a reference collection of 52 strains of the A. calcoaceticus-A. baumannii complex and 137 strains of other species resulted in an identification sensitivity and specificity of 100%. By using the array, the species distribution of 291 isolates of the A. calcoaceticus-A. baumannii complex from patients with bacteremia were determined to be A. baumannii (221 strains [75.9%]), Acinetobacter gen. sp. 3 (67 strains [23.0%]), Acinetobacter gen. sp. 13TU (2 strains [0.7%]), and unidentified Acinetobacter sp. (1 strain [0.3%]). The identification accuracy of the array for 12 randomly selected isolates from patients with bacteremia was further confirmed by sequence analyses of the ITS region and the 16S rRNA gene. Antimicrobial susceptibility testing of the 291 isolates from patients with bacteremia revealed that A. baumannii strains were less susceptible to antimicrobial agents than Acinetobacter gen. sp. 3. All Acinetobacter gen. sp. 3 strains were susceptible to ampicillin-sulbactam, imipenem, and meropenem; but only 67.4%, 90%, and 86% of the A. baumannii strains were susceptible to ampicillin-sulbactam, imipenem, and meropenem, respectively. The observed significant variations in antimicrobial susceptibility among different species in the A. calcoaceticus-A. baumannii complex emphasize that the differentiation of species within the complex is relevant from a clinical-epidemiological point of view.

Published ahead of print on 2 April 2008.