Annals of Clinical Microbiology, The official Journal of the Korean Society of Clinical Microbiology


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pISSN 2288-0585 eISSN 2288-6850

Molecular Epidemiology of Infection Caused by OXA-23 or IMP-1 β-Lactamase-Producing Acinetobacter baumannii

Original article

Annals of Clinical Microbiology (Ann Clin Microbiol) 2005 December Volume 8, Issue 2, pages 121-129.

Molecular Epidemiology of Infection Caused by OXA-23 or IMP-1 β-Lactamase-Producing Acinetobacter baumannii

Kwang Ok Park1, Han Chul Son2, Il Kwon Bae3, and Seok Hoon Jeong3
Department of Quality Improvement, Pusan National University Hospital1; Department of Laboratory Medicine, Pusan National University College of Medicine2; and Department of Laboratory Medicine, Kosin University College of Medicine3, Busan, Korea


Background: The purposes of this study were to investigate the prevalence of imipenem-resistant clinical Acinetobacter baumannii isolates and to determine the mechanism of the resistance. 

Methods: During the period of June to September 2004, susceptibility to imipenem of A. baumannii isolates from a hospital in Busan, Korea were investigated. The isolates were screened for the production of carbapenemase and metallo-β-lactamase by Modified-Hodge and EDTA-disk synergy tests, respectively; minimum inhibitory concentrations (MICs) were determined by agar dilution method. Genes coding for GES, IMP, VIM, SMP-1, GIM-1 and OXA type β-lactamases were searched by PCR amplification, and the PCR products were subjected to direct sequencing. Isoelectric points of β-lactamases were estimated by isoelectric focusing and the epidemiological relationships of isolates were investigated by enterobacterial repetitive intergenic consensus (ERIC) PCR.

Results: Fifty eight strains of A. baumannii were isolated from clinical specimens during the surveillance period, and 14 isolates (24.1%) were resistant to imipenem. Of the 14 isolates, 9 were tested positive in Modified-Hodge test and 2 were also positive in EDTA-disk synergy test. Genes encoding OXA-23 and IMP-1 were detected in 7 and 2 isolates, respectively. In IEF studies, OXA-23 and IMP-1 enzymes had corresponding pIs at 6.7 and 9.0, respectively. Seven OXA-23-producing and 2 IMP-1-producing isolates showed the same ERIC PCR patterns. 

Conclusion: It is concluded that 7 and 2 A. baumannii isolates from the patients in a hospital in Busan acquired resistance to imipenem by producing OXA-23 and IMP-1 β-lactamases, respectively. The isolates producing these β-lactamases might be originated from a common source. (Korean J Clin Microbiol 2005;8(2):105-112)


Acinetobacter baumannii, OXA-23, IMP-1, Imipenem-resistance