Rapid Identification of New Delhi Metallo-β-Lactamase (NDM) Using Tryptic Peptides and LC-MS/MS.Antimicrob Agents Chemother 2019AA
There is significant interest in the development of mass spectrometry (MS) methods for antimicrobial resistance protein detection, given the ability of these methods to confirm protein expression. In this work, we studied the performance of a liquid chromatography, tandem MS multiple reaction monitoring (LC-MS/MS MRM) method for the direct detection of the New Delhi Metallo-β-Lactamase (NDM) carbapenemase in clinical isolates. Using a genoproteomic approach, we selected three unique peptides (SLGNLGDADTEHYAASAR, AFGAAFPK and ASMIVMSHSAPDSR) specific to NDM that were efficiently ionized and spectrally well-defined. These three peptides were used to build an assay with turnaround time of 90 minutes. In a blinded set, the assay detected 21/24 blaNDM -containing and 76/76 negative isolates, corresponding to a sensitivity of 87.5% (95% CI 67.6%-97.3%) and a specificity of 100% (95% CI; 95.3-100%). One of the missed identifications was determined by protein fractionation to be due to low NDM protein expression (∼0.1fm/μg), below the assay limit of detection. Parallel disk diffusion susceptibility testing demonstrated this isolate to be meropenem susceptible, consistent with low NDM expression. Total proteomic analysis of the other two missed identifications did not detect NDM peptides, but detected other proteins expressed from the blaNDM -containing plasmids, confirming plasmids were not lost. The measurement of relative NDM concentrations over the entire isolate test set demonstrated variability spanning four orders of magnitude, further confirming the remarkable range that may be seen in NDM expression. This study highlights the sensitivity of LC-MS/MS to variations in NDM protein expression with implications for how this technology may be used.