JAC Advance Access published online on February 6, 2007
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkl544
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IMP-4 and OXA ß-lactamases in Acinetobacter baumannii 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
Received 4 October 2006; returned 13 November 2006; revised 23 November 2006; accepted 12 December 2006
* Corresponding author. Tel: +65-6321-4505; Fax: +65-6222-6826; E-mail: koh.tse.hsien{at}sgh.com.sg
OBJECTIVE: To compare the incidence of carbapenemase genes in Acinetobacter baumannii between two time periods.
METHODS: We studied 114 isolates of imipenem-resistant A. baumannii collected over two 5 month periods (in 1996 and 2001). Isolates showing carbapenemase activity by plate bioassay were screened for carbapenemase genes using PCR. Chromosomal DNA from strains carrying carbapenemase genes was subjected to PFGE after digestion with ApaI.
RESULTS: The incidence of imipenem-resistant A. baumannii in our hospital rose from 1.1 per 1000 admissions in 1996 to 2.3 per 1000 admissions in 2001. However, the number of carbapenemase-producing A. baumannii rose only slightly in 2001 (0.8 per 1000 admissions) compared to 1996 (0.5 per 1000 admissions). Of 44 isolates with carbapenemase activity, 4 isolates carried blaIMP-4, 5 carried blaOXA-58, and 40 carried blaOXA-23. In addition, most isolates carried a blaOXA-51-type ß-lactamase gene. All strains with blaIMP-4, also carried blaOXA-58 and blaPSE-1, but not blaOXA-51-type ß-lactamase genes. PCR analysis repeated on seven recent isolates of susceptible A. baumannii showed only the presence of blaOXA-51-type ß-lactamase genes. A total of five novel blaOXA-51-type ß-lactamase genes (blaOXA-88,-91,-93,-94, and -95) and one new blaOXA-58-type ß-lactamase gene (blaOXA-96) were found.
CONCLUSIONS: The incidence of carbapenemase genes did not vary significantly between the two study periods. There is a wide diversity of OXA genes in A. baumannii in Singapore. The most common carbapenemase gene found in our study was blaOXA-23.
Key Words: carbapenemase , metallo-ß-lactamase , resistance
Present address. Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074, Singapore
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