Bacterial Strain Differentiation by Mass Spectrometry

Randy J. Arnold, Jonathan A. Karty, and James P. Reilly 

Identification of Microorganisms by Mass Spectrometry, Edited by Charles L. Wilkins and Jackson O. Lay, Jr. 

When our group began working with bacteria samples in 1996, the first question we were interested in was whether high-resolution MALDI-TOF mass spectrometry would enable us to resolve far more peaks in bacteria mass 

Encouraged by this spectral reproducibility, we focused our efforts on the particularly challenging problem of distinguishing bacterial strains by MALDI MS. We developed a modified correlation approach22 that relies on two fundamental qualities of bacterial mass spectra. First, because different bacterial strains of the same species have substantial, if not complete, genetic overlap, most of the protein masses observed with two different strains will be identical. This feature limits the value of the biomarker approach that is commonly used to differentiate bacteria species. Second, as just noted, closely controlled sample preparation and mass analysis procedures can result in highly reproducible results.22 The modified correlation approach takes advantage of subtle, yet reproducible, differences in mass spectra obtained from dif- 

Application of the modified cross-correlation method was successfully demonstrated by comparing four independently recorded spectra with a library of spectra from 25 different strains of E. coli.22 These four strains were chosen arbitrarily without prior knowledge of the results. Three of the spectra of these strains used to compare to the library were obtained from cultures other than those used to generate their corresponding library spectra. The 

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