JAC Advance Access originally published online on September 3, 2007
Journal of Antimicrobial Chemotherapy 2007 60(5):1173-1174; doi:10.1093/jac/dkm334
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Correspondence |
Carbapenemase and efflux pump genes in Acinetobacter calcoaceticus–Acinetobacter baumannii complex strains from Singapore
1 Department of Pathology, Singapore General Hospital, Outram Road, Singapore 169608, Singapore 2 Department of Internal Medicine, Singapore General Hospital, Outram Road, Singapore 169608, Singapore 3 Department of Clinical Research, Singapore General Hospital, Outram Road, Singapore 169608, Singapore
* Corresponding author. Tel: +65-6321-4275; Fax: +65-6222-6826; E-mail: koh.tse.hsien{at}sgh.com.sg
Keywords: metallo-ß-lactamase , IMP , OXA
We recently published a paper describing the distribution of OXA and IMP ß-lactamases in Acinetobacter spp. from Singapore.1 Since that manuscript was submitted, there has been accumulating evidence suggesting that OXA-51-type ß-lactamases are ubiquitous in Acinetobacter baumannii sensu stricto.2
To resolve the identity of isolates from our original study that were identified using biochemical tests as A. baumannii, but were negative for blaOXA-51-type genes, we used PCR to re-test all 12 strains using a new set of universal blaOXA-51-type primers.3 We also sequenced the 16S rDNA gene (first 500 bp) using primer 8FPL described by Relman4 and in-house primer 515R (5'-TTA CCG CGG CAG CTG GCA C-3'), and the 16–23S rRNA gene intergenic spacer using the primers described by Chang et al.5 In addition, we tested for the presence of the efflux genes adeB, adeE and adeY using the primers described by Chu et al.,6 since it has been shown that the AdeABC multidrug efflux pumps are intrinsic to A. baumannii, whereas the AdeDE and AdeXY pumps are found predominantly in Acinetobacter genomospecies 3.
The final definition of strains to species level was based primarily on the 16–23S rRNA gene intergenic spacer sequences but also took into consideration the results of all the other tests (Table 1). Five strains were positive for blaOXA-51-type genes with the new primer set and remain identified as A. baumannii. Another five strains were re-identified as either Acinetobacter genomospecies 3 or Acinetobacter genomospecies 13TU. Conflicting results did not allow us to discriminate within the Acinetobacter calcoaceticus–Acinetobacter baumannii complex for two isolates.
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The segregation of carbapenemase genes between the different Acinetobacter genomospecies is striking (Table 1). Of particular note, the IMP-4 metallo-ß-lactamase is found in either Acinetobacter genomospecies 3 or Acinetobacter genomospecies 13TU but not in A. baumannii. Our data do support the hypothesis that blaOXA-51-type genes are intrinsic to A. baumannii. The distribution of efflux genes is also consistent with that reported by Chu et al.6
The A. calcoaceticus–A. baumannii complex is composed of four closely related species (A. calcoaceticus, A. baumannii, Acinetobacter genomospecies 3 and Acinetobacter genomospecies 13TU), which are difficult to differentiate phenotypically using traditional laboratory biochemical tests and commercial kits. In routine clinical practice, this distinction between the species is not usually clinically relevant and is rarely attempted. However, it may be important to define members of the A. calcoaceticus–A. baumannii complex to species level when describing the presence of ß-lactamases and other resistance determinants. As Turton et al.2 suggest, ß-lactamase-gene-specific PCR may be a good way to speciate Acinetobacter spp.
The 16S rDNA and 16–23S rRNA gene intergenic spacer sequences were deposited in GenBank under the following accession numbers EU030630–EU030641 and EU030647–EU030658.
None to declare.
This study was funded by a Singhealth Cluster Research Grant EX012/2001.
Footnotes
Present address. Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074, Singapore. 
References
1
Koh TH, Sng LH, Wang GC, et al. IMP-4 and OXA ß-lactamases in Acinetobacter baumannii from Singapore. J Antimicrob Chemother (2007) 59:627–32.
2
Turton JF, Woodford N, Glover J, et al. Identification of Acinetobacter baumannii by detection of the blaOXA-51-like carbapenemase gene intrinsic to this species. J Clin Microbiol (2006) 44:2974–6.
3 Woodford N, Ellington MJ, Coelho JM, et al. Multiplex PCR for genes encoding prevalent OXA carbapenemases in Acinetobacter spp. Int J Antimicrob Agents (2006) 27:351–3.[CrossRef][Web of Science][Medline]
4 Relman DA. Universal bacterial 16S rDNA amplification and sequencing. In: Diagnostic Molecular Microbiology: Principles and Applications—Persing DH, Smith TF, Tenover FC, et al, eds. (1993) Washington, DC: American Society for Microbiology. 489–95.
5
Chang HC, Wei YF, Dijkshoorn L, et al. Species-level identification of isolates of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex by sequence analysis of the 16S-23S rRNA gene spacer region. J Clin Microbiol (2005) 43:1632–9.
6
Chu YW, Chau SL, Houang ET. Presence of active efflux systems AdeABC, AdeDE and AdeXYZ in different Acinetobacter genomic DNA groups. J Med Microbiol (2006) 55:477–8.
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