Potential and limitations of MALDI-TOF MS for discrimination within the species Leuconostoc mesenteroides and Leuconostoc pseudomesenteroides

The discriminatory power of MALDI-TOF MS (matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry) was evaluated for differentiation of bacterial strains within Leuconostoc mesenteroides and Leuconostoc pseudomesenteroides species. Protein fingerprints were generated with MALDI-TOF MS for 24 Leuconostoc strains and analyzed with ClinProTools at species level and below. A treatment of bacterial cells prior to MALDI-TOF MS analysis was optimized applying different lysozyme concentrations. A pre-treatment with a lysozyme concentration of 12.5 mu g ml(-1) for 30 min exposure time enhanced the reproducibility of the spectra but did not influence the cluster analysis in ClinProTools. The cluster analysis resulted in the identification of seven different peak patterns shared among twelve strains of L. pseudomesenteroides and eight peak patterns shared among twelve strains of L. mesenteroides. The protein fingerprints of 24 Leuconostoc strains were sufficiently diverse for a reliable discrimination of half of the analyzed starter cultures at strain level. The other half of the strains could only be identified at cluster level. The discrimination at subspecies level was not possible on the basis of MALDI-TOF MS profiling. The MALDI-TOF MS methodology delivered interesting information about the diversity of bacterial isolates belonging to the two species L. mesenteroides and L. pseudomesenteroides but had its limitations for subspecies discrimination of unknown isolates as well as strain identification.