Korean J Lab Med.  2011 Oct;31(4):265-270. 10.3343/kjlm.2011.31.4.265.

Antimicrobial Resistance Determinants in Imipenem-nonsusceptible Acinetobacter calcoaceticus-baumannii Complex Isolated in Daejeon, Korea

• Sung JY
• Kwon KC
• Cho HH
• Koo SH

• KMID: 1781690
• DOI: http://doi.org/10.3343/kjlm.2011.31.4.265

Abstract

BACKGROUND
Members of the Acinetobacter calcoaceticus-baumannii (Acb) complex are important opportunistic bacterial pathogens and present significant therapeutic challenges in the treatment of nosocomial infections. In the present study, we investigated the integrons and various genes involved in resistance to carbapenems, aminoglycosides, and fluoroquinolones in 56 imipenem-nonsusceptible Acb complex isolates.
METHODS
This study included 44 imipenem-nonsusceptible A. baumannii, 10 Acinetobacter genomic species 3, and 2 Acinetobacter genomic species 13TU strains isolated in Daejeon, Korea. The minimum inhibitory concentrations (MICs) were determined by Etest. PCR and DNA sequencing were used to identify the genes that potentially contribute to each resistance phenotype.
RESULTS
All A. baumannii isolates harbored the blaOXA-51-like gene, and 21 isolates (47.7%) co-produced OXA-23. However, isolates of Acinetobacter genomic species 3 and 13TU only contained blaIMP-1 or blaVIM-2. Most Acb complex isolates (94.6%) harbored class 1 integrons, armA, and/or aminoglycoside-modifying enzymes (AMEs). Of particular note was the fact that armA and aph(3')-Ia were only detected in A. baumannii isolates, which were highly resistant to amikacin (MIC50> or =256) and gentamicin (MIC50> or =1,024). In all 44 A. baumannii isolates, resistance to fluoroquinolones was conferred by sense mutations in the gyrA and parC. However, sense mutations in parC were not found in Acinetobacter genomic species 3 or 13TU isolates.
CONCLUSIONS
Several differences in carbapenem, aminoglycoside, and fluoroquinolone resistance gene content were detected among Acb complex isolates. However, most Acb complex isolates (87.5%) possessed integrons, carbapenemases, AMEs, and mutations in gyrA. The co-occurrence of several resistance determinants may present a significant threat.

Keyword

Acinetobacter baumannii; Acinetobacter genomic species; Carbapenemase; Integron

MeSH Terms

Acinetobacter Infections/microbiology
Acinetobacter baumannii/*genetics/isolation & purification
Anti-Bacterial Agents/*pharmacology
Bacterial Proteins/genetics
DNA Gyrase/genetics
DNA, Bacterial/chemistry/genetics
Drug Resistance, Bacterial/*genetics
Humans
Imipenem/*pharmacology
Integrons/genetics
Methyltransferases/genetics
Microbial Sensitivity Tests
Mutation
Polymerase Chain Reaction
Republic of Korea
Sequence Analysis, DNA
beta-Lactamases/biosynthesis/genetics

Figure

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  Fig. 1 Schematic representation of gene cassette structures located in the class 1 integron isolated from Acinetobacter calcoaceticus-baumannii complex isolates. The horizontal arrows indicate the translation orientation of the genes.

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  Fig. 2 Repetitive extragenic palindromic (REP)-PCR patterns of genomic DNA from imipenem-nonsusceptible Acinetobacter calcoaceticus-baumannii complex isolates. Lane M, 1-kb DNA size marker; Ab, Acinetobacter baumannii; Ag, Acinetobacter genomic species 3.

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