Rapid detection of metallo-β-lactamase-producing by the combination of MALDI-TOF MS and CarbaNP.

Aims: Carbapenem resistance in is emerging and is mainly attributed to insertion sequence (IS)-mediated activation of the carbapenemase gene . We investigated the use of matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and the CarbaNP assay for the rapid identification of these strains.

Methods: This study used the Bruker MALDI Biotype system and the mass spectra models generated by 20 reference strains (10 -positive and 10 -negative) in the ClinProTools software to identify 404 (71 -positive and 333 -negative) clinical isolates. The ability of the CarbaNP assay to detect IS-mediated activation of the gene was assessed and the results obtained by molecular analysis were used as reference methods.

Results: The support vector machine model generated by ClinProTools was found to be the most reliable algorithm for differentiation of -positive and -negative subgroups. Using the direct transfer method, all but one -negative isolates were correctly identified to the two subgroups by the model. The correct identification of the -negative isolate was obtained upon retesting by the extraction method. Of the 81 -positive isolates, PCR and sequencing showed that 30 had an IS element providing the promoter for activation of . With regard to the presence of the IS element, the CarbaNP test in the upstream region had 100% sensitivity, 80.4% specificity, 75.0% positive predictive value and 100% negative predictive value.

Conclusions: The combination of MALDI-TOF MS and the CarbaNP assay can be applied in diagnostic clinical laboratory for rapid identification of with IS element-activated gene.