Universal sample preparation method for characterization of bacteria by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Mass spectrometry has been a very useful method to rapidly identify microorganisms associated with infectious diseases, detect bioterrorism threats, and discriminate among different subtypes of a pathogen. In this study, we developed a universal method for bacterial identification by matrix-assisted laser desorption ionization-time of flight mass spectrometry. The effects on the mass spectrum of different experimental conditions, including the amount of bacterial cells used and treatment procedures with different solutions, matrix species, and solvents, were examined, and an optimized protocol was developed. Several different bacterial species, including Yersinia pestis, Escherichia coli, Burkholderia cepacia, Bacillus anthracis, and Staphylococcus aureus, which covered the gram-negative and -positive species and spore-producing and non-spore-producing species, were analyzed to evaluate the utility of the protocol. The results showed that five different species and different strains of the same species (9 strains of S. aureus and 10 strains of E. coli) could be discriminated clearly by their peak profiles in a mass range of 1,000 to 20,000 Da. This protocol is simple, rapid, and easy to perform; has excellent reproducibility; and is suitable for the construction of a mass spectrum fingerprinting database, which helps in fast bacterial identification via database searching.