From the Research
The recommended method for metallo-beta-lactamase (MBL) gene detection is molecular testing, particularly polymerase chain reaction (PCR) assays. While CLSI does not recommend the imipenem + EDTA method due to reliability concerns, PCR directly targets and amplifies specific MBL genes such as NDM, VIM, IMP, and SPM, providing definitive identification. This molecular approach offers higher sensitivity and specificity compared to phenotypic methods, as noted in a recent review on metallo-beta-lactamases 1. For implementation, laboratories should use validated PCR protocols with appropriate primers targeting common MBL variants, followed by gel electrophoresis or real-time PCR for detection. Sequencing can provide additional confirmation when needed. Molecular detection is preferred because it identifies the specific MBL gene present, which has epidemiological importance and can guide infection control measures. Additionally, multiplex PCR assays allow simultaneous detection of multiple resistance genes, making this approach both efficient and definitive for MBL identification in carbapenem-resistant organisms. Some studies have evaluated phenotypic detection methods, including the use of imipenem-EDTA combined disk tests 2, 3, 4, but these methods have limitations in terms of sensitivity and specificity. A more recent study highlights the challenges posed by MBLs and the need for effective diagnostic tools and treatment options 5. Overall, molecular testing, specifically PCR assays, is the most reliable method for MBL gene detection, and its use is supported by the most recent and highest quality evidence 1.