Microorganism identification by mass spectrometry and protein database searches

A method for rapid identification of microorganisms is presented, which exp loits the wealth of information contained in prokaryotic genome and protein sequence databases. The method is based on determining the masses of a set of ions by MALDI TOF mass spectrometry of intact or treated cells. Subsequ ent correlation of each ion in the set to a protein, along with the organis mic source of the protein, is performed by searching an Internet-accessible protein database. Convoluting the lists for all ions and ranking the organ isms corresponding to matched ions results in the identification of the mic roorganism. The method has been successfully demonstrated on B, subtilis an d E, coli, two organisms with completely sequenced genomes, The method has been also tested for identification from mass spectra of mixtures of microo rganisms, from spectra of an organism at different growth stages, and from spectra originating at other laboratories. Experimental factors such as MAL DI matrix preparation, spectral reproducibility, contaminants, mass range, and measurement accuracy on the database search procedure are addressed too . The proposed method has several advantages over other MS methods for micr oorganism identification.