Rapid discrimination of bacteria by matrix-assisted laser desorption/ionization mass spectrometry for maintenance of bacterial culture collections

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is beginning to play an important role in a rapid discrimination of bacteria, where ribosomal proteins composed of more than 50 subunits is used as biomarkers. In this study, this technique was applied to the maintenance of bacterial culture collections. It was confirmed that most of the biomarker peaks could be observed in the whole cell lysate of model lactic acid bacteria, which was prepared simply by bead-beating and centrifugation. The mass differences of specific ribosomal subunit proteins observed on the MALDI mass spectra allowed us to discriminate two lactic acid bacteria at a subspecies level difference (Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris). By comparing the MALDI mass spectrum of the stored culture of Lc. lactis subsp. lactis with that of the pure culture as a reference, it could be easily found that the stored culture was cross-contaminated with other lactic acid bacteria.