Korean J Lab Med.  2010 Oct;30(5):498-506. 10.3343/kjlm.2010.30.5.498.

Genetic Basis of Multidrug-resistant Acinetobacter baumannii Clinical Isolates from Three University Hospitals in Chungcheong Province, Korea

• Koo SH
• Kwon KC
• Cho HH
• Sung JY

• KMID: 1022041
• DOI: http://doi.org/10.3343/kjlm.2010.30.5.498

Abstract

BACKGROUND
The emergence of multidrug-resistant (MDR) Acinetobacter baumannii as an important opportunistic pathogen has given rise to significant therapeutic challenges in the treatment of nosocomial infections. In the present study, we assess the antibiotic resistance mechanisms of MDR A. baumannii strains by estimating the prevalence of antibiotic resistance determinants, including integrons, beta-lactamases, str genes, and gyrA and parC mutations.
METHODS
Thirty-five MDR A. baumannii clinical isolates were collected from 3 Korean university hospitals over a 2-yr period. A. baumannii was confirmed by rpoB gene analysis. For each isolate, the minimal inhibitory concentrations (MICs) of 9 antibiotics were determined by the agar dilution method. PCR and DNA sequencing were used to identify the genes that potentially contribute to each resistance phenotype.
RESULTS
Of the 35 MDR A. baumannii isolates examined, 7 antibiotic resistance gene determinants were detected. These resistance gene determinants included the gene bla(OXA-23), with an upstream element ISAba1 to promote increased gene expression and subsequent resistance to carbapenems, in 8 isolates (22.9%); aacA4, located within class 1 integrons, in 7 isolates (20.0%); and fluoroquinolone resistance conferred by gyrA and parC sense mutations in 31 isolates.
CONCLUSIONS
Of the 35 MDR A. baumannii isolates, 26 (74.3%) from both outbreak and sporadic cases possessed at least 4 of the 7 antibiotic resistance gene determinants that give rise to the MDR phenotype. The co-occurrence of several resistance determinants may present a significant threat.

Keyword

MDR A. baumannii; Antibiotic resistance gene determinants; ISAba1

MeSH Terms

Acinetobacter baumannii/*drug effects/*genetics/isolation & purification
Anti-Bacterial Agents/*pharmacology
Bacterial Proteins/*genetics
Carbapenems/pharmacology
Drug Resistance, Multiple, Bacterial/*genetics
Hospitals, University
Humans
Integrons/genetics
Microbial Sensitivity Tests
Republic of Korea
Sequence Analysis, DNA

Figure

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  Fig. 1. Schematic representation of the gene cassette structure located in the class 1 integron isolated from multidrug-resistant Acinetobacter baumannii. The horizontal arrows indicate the translation orientation of the genes.

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  Fig. 2. Repetitive element sequence-based (REP)-PCR patterns of genomic DNA from 35 multidrug resistant A. baumannii. Lane M contains a 1 kb DNA size marker.

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