Direct mass spectrometric analysis of Bacillus spores

Spores from the Bacillus species, B. cereus, B. anthracis B. thuringensis, B. lichenformis, B, globigi, and B, subtilis, were examined by direct probe mass spectrometry using electron ionization (EI) and positive and negative chemical ionization (CI). Molecular ions from free fatty acids and nucleic acids were observed in the 70eV spectra as were fragments from glycerides. Spectra obtained with isobutane positive chemical ionization (CI+) were do minated by ions associated with pyranose compounds such as N-acetylglucosam ine (NAG). Unlike the positive ion spectra, the negative ion spectra of the spores were very simple and contained few peaks. The M- ion from dipicolin ic acid (DPA) was the base peak in the negative ion spectra of all spore sp ecies except those from B, lichenformis, The negative ion of DPA produced s uch a strong signal that 10(8) colony forming units (CFUs) of B. cereus spo res could be detected directly in 0.5 g of ground rice. Principal component analysis (PCA) of the spectra revealed that only CI+ spectra contained dif ferences that could be used to identify the spectra by species. Differentia tion of the CI+ spectra by PCA. was attributed to variances in the peaks as sociated with the bacterial polymer paly(3-hydroxybutyrate) (PHB) and NAG. Similar differences in PHB and NAG peaks were detected in the CI+ spectra o f a suite of vegetative Bacillus stains grown with various media. Copyright (C) 1999 John Wiley & Sons, Ltd.