Discrimination between bacterial spare types using time-of-flight mass spectrometry and matrix free infrared laser desorption and ionization

We demonstrate that molecular ions with mass-to-charge ratios (m/z) ranging from a few hundred to 19 050 can be desorbed from whole bacterial spores u sing infrared laser desorption and no chemical matrix. We have measured the mass of these ions using time-of-flight mass spectrometry and we observe t hat different ions are desorbed from spores of Bacillus cereus, Bacillus th uringiensis, Bacillus subtilis, and Bacillus niger. Our results raise the p ossibility of identifying microorganisms using mass spectrometry without co nventional sample preparation techniques such as the addition of a matrix. We have measured the dependence of the ion yield from B. subtilis on desorp tion wavelength over the range 3.05-3.8 mum, and we observe the best result s at 3.05 mum, We have also generated mass spectra from whole spores using 337-mm ultraviolet laser desorption, and we find that these spectra are inf erior to spectra generated with infrared desorption. Since aerosol analysis is a natural application for matrix-free desorption, we have measured mass spectra from materials such as ragweed pollen and road dust that are likel y to form a background to microbial aerosols. We find that these materials are readily differentiated from bacterial spores.