A highly sensitive carbapenemase assay using laser desorption/ionization mass spectrometry based on a parylene-matrix chip

•A quantitative carbapenemase assay was developed using LDI-MS with a parylene-matrix chip.•Reproducibility (spot-to-spot and shot-to-shot) of LDI-MS was presented with carbapenems.•A carbapenem-susceptibility test was carried out using 51 bacterial strains.•LDI-MS presented more sensitive and selective results than conventional MALDI-TOF MS.

A quantitative carbapenemase assay was developed using laser desorption/ionization mass spectrometry (LDI-MS) based on a parylene-matrix chip. As a first step, the reproducibility (spot-to-spot, shot-to-shot, and day-to-day) of LDI-MS based on a parylene-matrix chip and the quantification ranges for four carbapenem antibiotics (doripenem, ertapenem, imipenem, and meropenem) were determined. A carbapenem-susceptibility test was performed using the four carbapenems and 51 bacterial strains that displayed (1) carbapenem resistance with carbapenemase, (2) carbapenem resistance without carbapenemase, or (3) carbapenem susceptibility. The susceptibility test results showed that LDI-MS based on a parylene-matrix chip was more sensitive and selective for detecting the carbapenemase reaction than conventional MALDI-TOF MS based on a 2,5-dihydroxybenzoic acid matrix.

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