title: MALDI-TOF MS applied to indirect carbapenemase detection: a validated procedure to clearly distinguish between carbapenemase-positive and carbapenemase-negative bacterial strains.
abstract: 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.
authors.affiliation: Department of Laboratory Medicine, Beijing Tongren Hospital, No. 1. Dongjiaominxiang Road, Dongcheng District, Beijing 100730, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Wang
authors.forename: Chao
authors.initials: C
authors.lastname: Han
authors.forename: Wenjun
authors.initials: W
authors.lastname: Sui
authors.forename: Mei
authors.initials: M
authors.lastname: Wang
authors.forename: Xinxin
authors.initials: X
authors.lastname: Lu
mesh_terms: D001419:Bacteria / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001618:beta-Lactamases; C063912:carbapenemase