Direct Identification of IMP and VIM Metallo-β-Lactamases in Gram-Negative Bacteria Using A-MALDI

Rapid and accurate identification of carbapenemase-producing Enterobacteriaceae (CPE) is crucial for effective infection control and patient treatment. However, accurate identification of VIM and IMP metallo-β-lactamases remains still challenging using MALDI-TOF MS.

The A-MALDI method which incorporates sequential lysis steps and internal mass calibration, was used for the identification of IMP and VIM carbapenemases. Two Escherichia coli standard strains and 26 clinical isolates harboring IMP or VIM genes were tested by A-MALDI along with corresponding negative controls. Previously published carbapenemases-negative data (n = 112) were used to check the specificity of IMP and VIM identification.

For IMP-positive isolates, proteoforms corresponding to amino acid residues 20-246 showed distinct peaks for IMP. For VIM-positive isolates, unique single peaks corresponding to amino acid residues 27-266 allowed clear identification of VIM. Clinical evaluation of A-MALDI demonstrated 93.9% accuracy for IMP identification (100% sensitivity, 93.3% specificity) and 100% accuracy for VIM identification.

This study successfully expands the direct identification capabilities for VIM and IMP, achieving comprehensive identification of all six carbapenemases using A-MALDI. We anticipate that A-MALDI will provide clinical laboratories with a powerful tool for rapid identification of all types of carbapenemases in bacterial infections.