Korean J Clin Microbiol.  2011 Jun;14(2):67-73. 10.5145/KJCM.2011.14.2.67.

Characterization of Acinetobacter baumannii Co-producing Carbapenemases OXA-23 and OXA-66, and armA 16S Ribosomal RNA Methylase at a University Hospital in South Korea

• Jeong HW
• Son BR
• Shin DI
• Ryu D
• Hong SB
• Han K
• Shin KS

• KMID: 2089817
• DOI: http://doi.org/10.5145/KJCM.2011.14.2.67

Abstract

BACKGROUND
In the present study, the resistance mechanisms against carbapenems and aminoglycosides for 23 strains of multi-drug-resistant Acinetobacter baumannii isolated at a university hospital were investigated.
METHODS
The minimal inhibitory concentrations (MICs) were determined via broth microdilution or Etest. The genes encoding OXA-type carbapenemases and 16S rRNA methylase were identified using multiplex PCR, and the amplified products were sequenced. Conjugation experiments were conducted, and an epidemiologic study was performed using enterobacterial repetitive intergenic consensus (ERIC)-PCR.
RESULTS
In the isolates, the MICs of the tested aminoglycosides, including arbekacin, were >1024 microg/mL; the MICs of aztreonam, cefepime, ceftazidime, and ciprofloxacin ranged from 64 to 128 microg/mL; and the MICs of carbapenem ranged from 32 to 64 microg/mL, as determined through the broth microdilution test. According to the E-test, the MICs of ampicillin/sulbactam and colistin were 8 and 0.25 to 0.38 microg/mL, respectively. Sequence analysis confirmed that all of the isolates expressed carbapenemases OXA-23 and OXA-66, as well as armA 16S rRNA methylase. In addition, ISAba1 was identified upstream of the gene encoding OXA-23. OXA-23 and armA were not transferred to Escherichia coli J53 cells in the transconjugation experiments. ERIC-PCR molecular fingerprinting produced a single pattern in all cases.
CONCLUSION
The co-production of OXA-23 and armA 16S rRNA methylase may be attributed to the multidrug resistance of the A. baumannii isolates in the present study. Stricter surveillance and more rapid detection are necessary to prevent the spread of this type of resistance in the future.

Keyword

Acinetobacter baumannii; armA; Outbreak; OXA-23

MeSH Terms

Acinetobacter
Acinetobacter baumannii
Aminoglycosides
Aztreonam
Carbapenems
Ceftazidime
Cephalosporins
Ciprofloxacin
Colistin
Consensus
Dermatoglyphics
Dibekacin
Drug Resistance, Multiple
Epidemiologic Studies
Escherichia coli
Methyltransferases
Multiplex Polymerase Chain Reaction
Republic of Korea
RNA, Ribosomal, 16S
Sequence Analysis
Aminoglycosides
Aztreonam
Carbapenems
Ceftazidime
Cephalosporins
Ciprofloxacin
Colistin
Dibekacin
Methyltransferases
RNA, Ribosomal, 16S

Figure

• 

  Fig. 1. The finding of DNA fingerprints by ERIC-PCR of Acinetobacter baumannii clinical isolates. Clinical isolates with outbreak (lanes 2∼9) exhibits single DNA fingerprinting pattern but non-outbreak strains (lanes 10∼13) showed different patterns. Lane 1, molecular size marker (100 bp ladder); lanes 2∼9, clinical isolates of A. baumannii with outbreak; lanes 10∼13, clinical isolates of A. baumannii with non-outbreak strain, including cabapenem resistant A. baumannii isolated from other two University hospital; lane 14, molecular size marker (100 bp ladder).

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