Submitted to: Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2007
Publication Date: 7/13/2007
Publication URL: www3.interscience.wiley.com/cgi-bin/abstract/114291992/ABSTR
Citation: Meetani, M., Shin, Y., Zhang, S., Mayer, R.T., Basile, F. 2007. Desorption electrospray ionization mass spectrometry of intact bacteria. J. of Mass Spectrometry. Online. Interpretive Summary: There is a need to improve diagnostic/detection methods for microbes that might pose a threat to human, animal, and plant health. Early detection of pathogenic microorganisms can minimize the health hazards and spread of diseases. Mass spectrometric (MS) can provide alternatives to established detection methods as they can be faster and provide multidimensional data output. Common to all these approaches is the fact that bacterial samples require some type of pre-treatment in the form of extraction, digestion of protein-derived peptides, and/or mixing the microorganisms with a matrix compound and introducing them into mass spectrometer for direct analysis. A variety of samples have been analyzed by DESI-MS including peptides, proteins, bacteria , pharmaceutical samples, analytes separated on thin layer chromatography plates, natural products, forensic samples and chemical warfare agents. Recently, DESI-MS was applied to the analysis of several untreated microorganisms, yielding reproducible mass spectra useful for pattern recognition technique differentiation (Principal Components Analysis, PCA). The work reported here explores the use of DESI-MS to detect several different bacteria. The study shows that a large contribution to DESI-mass spectral fingerprint variation was the growth media preparation procedure. Conclusions are drawn from these findings in terms of strategies for rapid biodetection with DESI-MS.
Technical Abstract: Desorption electrospray ionization (DESI) mass spectrometry (MS) was used to differentiate 7 bacterial species based on their measured DESI-mass spectral profile. Both Gram positive and Gram negative bacteria were tested and included Escherichia coli, Staphyloccocus aureus, Enterococcus sp., Bordetella bronchiseptica, Bacillus thuringiensis, Bacillus subtilis and Salmonella typhimurium. Distinct DESI-mass spectra, in the mass range of 50 – 500 u, were obtained from whole bacteria in either positive or negative ion modes in less than 1 minute analysis time. Positive ion DESI-mass spectral fingerprints were compared using Principle Components Analysis (PCA) to investigate reproducibility for intra-day and day-to-day measurements and the method selectivity to differentiate the bacteria studied. Detailed study of the contributions to variances in the assay revealed that a large contribution to DESI-mass spectral fingerprint variation was the growth media preparation procedure. Specifically, experiments conducted with growth media prepared using the same batch yielded highly reproducible DESI-mass spectra, both in intra-day and in day-to-day analyses (i.e., one batch of growth media used over a 3-day period versus a new batch every day over the same 3-day period). Conclusions are drawn from our findings in terms of strategies for rapid biodetection with DESI-MS.