Phenotypic Detection of Carbapenem-Susceptible Metallo-β-Lactamase-Producing Gram-Negative Bacilli in the Clinical Laboratory

• Published in: Journal of Clinical Microbiology Vol. 44; no. 9; pp. 3139 - 3144
• Main Authors: Franklin, Clare, Liolios, Lisa, Peleg, Anton Y
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.09.2006
• Subjects: Acinetobacter - drug effects; Anti-Bacterial Agents - pharmacology; Bacteriological Techniques; Bacteriology; beta-Lactamases - genetics; beta-Lactamases - metabolism; Biological and medical sciences; Carbapenems - pharmacology; Culture Media; Enterobacteriaceae - drug effects; Fundamental and applied biological sciences. Psychology; Gram-Negative Bacteria - classification; Gram-Negative Bacteria - drug effects; Gram-Negative Bacteria - growth & development; Gram-Negative Bacterial Infections - microbiology; Humans; Infectious diseases; Laboratories; Medical sciences; Microbial Sensitivity Tests - instrumentation; Microbial Sensitivity Tests - methods; Microbiology; Phenotype; Polymerase Chain Reaction; Pseudomonas - drug effects; Sensitivity and Specificity; Hydrolases; β-Lactamase; Microbiology; Detection; Enzyme; Gram negative bacteria
• ISSN: 0095-1137; 1098-660X; 1098-5530
• DOI: 10.1128/JCM.00879-06

Rapid detection of metallo-β-lactamase (MBL)-producing gram-negative pathogens is critical to prevent their widespread dissemination. Thus far, no standardized phenotypic method is available, and previously reported techniques have poor sensitivity for detecting carbapenem-susceptible MBL-carrying isolates, an increasingly described phenomenon. We developed a phenotypic detection method using both a double-disk synergy test and a combined-disk test with imipenem and 292 μg EDTA on one agar plate. Genotypic confirmation was used for validation. Of the 134 clinical isolates, 84 were confirmed to carry an MBL. Of these, 51 (61%) were susceptible to at least one carbapenem, and 22 (26%) were isolated from blood. The phenotypic method correctly differentiated all MBL-producing isolates (sensitivity, 100%). Fifty-one of the 52 MBL-negative isolates were correctly differentiated (specificity, 98%). This study reports the validation of a simple and accurate MBL detection method that can be easily incorporated into the daily routine of a clinical laboratory. Early detection of MBL-carrying organisms, including those with susceptibility to carbapenems, is of paramount clinical importance, as it allows rapid initiation of strict infection control practices as well as therapeutic guidance for confirmed infection.