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Journal of Clinical Microbiology, April 2009, p. 1136-1142, Vol. 47, No. 4
0095-1137/09/$08.00+0     doi:10.1128/JCM.01592-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Evaluation of Phenotypic Tests for Detection of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Strains in China{triangledown}

Ting-ting Qu,1 Jun-li Zhang,1 Jie Wang,2 Jing Tao,1 Yun-song Yu,1* Ya-gang Chen,1 Jian-ying Zhou,2 and Lan-juan Li1

State Key Laboratory for Diagnosis and Treatment of Infectious Disease, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, China,1 Respiratory Department, First Affiliated Hospital, Medical School, Zhejiang University, Hangzhou, Zhejiang, China2

Received 16 August 2008/ Returned for modification 12 November 2008/ Accepted 2 February 2009

A total of 264 nonduplicate strains of imipenem (IPM)-nonsusceptible Pseudomonas aeruginosa were isolated from hospitals in 16 different regions throughout China. These 264 IPM-nonsusceptible clinical isolates of P. aeruginosa were examined by PCR, a metallo-β-lactamase (MBL) Etest, a double-disk synergy test (DDST), and a test using combined IPM disks supplemented with various amounts of EDTA. A total of 24 strains positive for MBLs were confirmed by PCR and DNA sequence analysis: 10 strains positive for the blaVIM-2 gene, 13 strains positive for the blaIMP-9 gene, and 1 strain positive for the blaIMP-1 gene. Real-time reverse transcriptase PCR (RT-PCR) was used to verify whether the isolates harboring MBL genes produced the enzyme and was considered the standard for evaluation of the methodology in this study. Of these 24 MBL-positive stains, 21 were confirmed as MBL-producing strains by real time RT-PCR for MBL expression and the other 3 had no expression of MBLs. The sensitivities, specificities, and positive and negative predictive values for the MBL Etest, the DDST, and the combined disk (CD) assay were evaluated. The best method for screening for MBL production in P. aeruginosa strains from China was the CD assay (IMP-EDTA) using 750 µg of EDTA/disk with a breakpoint of ≥6 mm. In the CD assay (IPM-EDTA) with 290 µg and 750 µg EDTA, the zone diameter increases for VIM-2-producing P. aeruginosa isolates were greater than those for IMP-9-producing P. aeruginosa isolates (P = 0.00).

* Corresponding author. Mailing address: State Key Laboratory for Diagnosis and Treatment of Infectious Disease, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, China. Phone and fax: 86 571 8723 6756. E-mail: yvys119{at}163.com

{triangledown} Published ahead of print on 11 February 2009.

Journal of Clinical Microbiology, April 2009, p. 1136-1142, Vol. 47, No. 4
0095-1137/09/$08.00+0     doi:10.1128/JCM.01592-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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