Research Paper

Analytical and Bioanalytical Chemistry

, Volume 405, Issue 15, pp 5259-5266

First online:

MALDI-TOF MS applied to indirect carbapenemase detection: a validated procedure to clearly distinguish between carbapenemase-positive and carbapenemase-negative bacterial strains

  • Lijun WangAffiliated withDepartment of Laboratory Medicine, Beijing Tongren Hospital
  • , Chao HanAffiliated withDepartment of Laboratory Medicine, Xi’an No. 1 Hospital
  • , Wenjun SuiAffiliated withDepartment of Laboratory Medicine, Beijing Tongren Hospital
  • , Mei WangAffiliated withDepartment of Laboratory Medicine, Beijing Tongren Hospital
  • , Xinxin LuAffiliated withDepartment of Laboratory Medicine, Beijing Tongren Hospital Email author 

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Laboratory identification of carbapenemase-producing clinical isolates is crucial to limit the spread of the bacteria. In this study, we shall first develop the matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI-TOF MS) assay in automatic identification of carbapenemase producers. A total of 143 well-characterized isolates were studied. After an incubation of bacteria with meropenem trihydrate, the mixture was centrifuged and the supernatant analyzed by MALDI-TOF MS. A genetic algorithm model with ClinProTools software was built using spectra of 43 carbapenemase-positive isolates and 40 carbapenemase-negative isolates after 2 h of incubation. This model was externally validated using 60 test isolates. All spectra of supernatants of the carbapenemase-negative isolates showed peak profiles comparable to that of pure meropenem (m/z 384.159, 406.140, and 428.122 of its two sodium salt variants) regardless of the incubation time tested. For the carbapenemase-positive isolates, the specific peak for meropenem at m/z 384.159 disappeared during the incubation time, two products of meropenem degradation were identified with m/z 358.18 (the decarboxylated product) and 380.161 (sodium salt of the decarboxylated product), and other degradation products were observed (native molecule with disrupted amide bond with m/z 402.169, three sodium salt variants with m/z 424.151, 446.133, and 468.115). Sixty test isolates were 100 % correctly classified as carbapenemase positive and carbapenemase negative with the genetic algorithm model. MALDI-TOF MS coupled with ClinProTools is capable of rapidly, accurately, and automatically identifying carbapenemase producers.

The average spectra of the carbapenemase-positive (red) and carbapenemasenegative isolates (green) were shown. Nine peaks differentiating the two classes are highlighted by arrows. x axis, mass per charge [m/z (in daltons)]; y axis, intensity(arbitrary units [arb.u.]).


MALDI Carbapenem Carbapenemases Resistance Classification