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Journal of Clinical Microbiology, September 2007, p. 2798-2801, Vol. 45, No. 9
0095-1137/07/$08.00+0     doi:10.1128/JCM.02486-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Convenient Test Using a Combination of Chelating Agents for Detection of Metallo-ß-Lactamases in the Clinical Laboratory

Center for Research in Anti-Infectives and Biotechnology, Department of Medical Microbiology & Immunology, Creighton University School of Medicine, 2500 California Plaza, Omaha, Nebraska 68178

Received 12 December 2006/ Returned for modification 14 March 2007/ Accepted 18 June 2007

Although transmissible metallo-ß-lactamases (MBLs) are a serious threat to ß-lactam antibiotic therapy, the CLSI currently does not recommend testing methods for the detection of MBLs. The aim of this study was to evaluate the capability of double-disk tests (DDTs) by using disks containing a combination of the chelators 2-mercaptopropionic acid (MPA) and Tris-EDTA (TE) to detect MBLs. Sixteen isolates (4 Acinetobacter baumannii isolates, 6 Pseudomonas aeruginosa isolates, 1 Serratia marcescens isolate, 1 Aeromonas hydrophila isolate, 1 Aeromonas veronii isolate, 2 Chryseobacterium meningosepticum isolates, and 1 Stenotrophomonas maltophilia isolate) producing IMP-1, IMP-1-like, IMP-18, GIM-1, SPM-1, VIM-2, VIM-2-like, and chromosomal MBLs and 20 isolates (7 Klebsiella pneumoniae isolates, 3 Escherichia coli isolates, 5 Enterobacter cloacae isolates, 2 S. marcescens isolates, 1 Proteus mirabilis isolate, and 2 A. baumannii isolates) producing non-MBL carbapenemases, AmpC ß-lactamases, and extended-spectrum ß-lactamases were tested. The DDT method was evaluated by using four types of chelator disks (TE, high-strength TE, MPA, and TE plus 20 µl of MPA [at various concentrations]) and the ß-lactams imipenem (IPM), meropenem (MEM), ertapenem (ERT), and ceftazidime (CAZ). DDTs with IPM and a TE disk supplemented with 1:320 MPA detected all MBLs and yielded no false-positive results. Some, but not all, MBL producers were detected in IPM-based tests involving the single chelator TE or MPA alone or by ERT- or CAZ-based tests. IPM-based tests with MPA concentrations other than 1:320 and all MEM-based tests had suboptimal sensitivities or specificities. DDT with IPM and a TE disk supplemented with 20 µl of 1:320 MPA appears to be convenient for the detection of MBLs in the clinical laboratory.

Published ahead of print on 27 June 2007.

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