Identification of micro-organisms, using MALDI-TOF-MS, uses a synthetic reference spectrum for comparison with the mass spectrum to register the micro-organism under study

摘要

Identifying micro-organisms uses matrix assisted laser desorption ionization/time of flight/mass spectrometry (MALDI-TOF-MS), is new. A database (DB) of reference spectra has mass spectra of some known micro-organisms. The reference spectrum (REF) uses synthetic reference spectra (REFS), which gather a reduced number of specific signals for a given micro-organism compared with natural mass spectra. Identifying micro-organisms by MALDI-TOF-MS, the signals from a synthetic reference spectrum contain at least one identification signal (Sid) relating to a single molecular cell component of each micro-organism. The molecular cell component is a peptide, protein, a ribonucleic acid (RNA) and/or a lipid, a ribosomal protein and especially a protein of a large ribosome sub-unit. The signals from a synthetic reference spectrum contain at least one empirical signal (Sem), specific for a given micro-organism, through comparison of the mass spectra of known micro-organisms. The comparison is visual and/or computer assisted. The criteria for the generation of an empirical signal are a given minimum frequency for the presence of a signal in a number of mass spectra for the same micro-organism, and a given minimum signal intensity. A signal is represented by a pair of coordinates composed of a mass or a mass/charge ratio as the X-coordinate, and an absolute or relative intensity as the Y-coordinate. The synthetic reference spectrum gives 5-30 signals and preferably 10-15. The mass spectra are registered from cells which have not been prepared. The analysis of the similarity of the mass spectra of the micro-organisms to be identified with the reference spectra stored in the database is restricted to a comparison of the signals contained in the reference spectra. The analysis of the similarity of the signals in the reference spectra uses weighting.