Differentiation of Microorganisms Based on Pyrolysis-Ion Trap Mass Spectrometry Using Chemical Ionization

Abstract

The ability to differentiate microorganisms using pyrolysision trap mass spectrometry was demonstrated for five Gram-negative disease-causing organisms: Brucella melitensis, Brucella suis, Vibrio cholera, Yersinia pestis, and Francisella tularensis. Bacterial profiles were generated for gamma-irradiated bacterial samples using pyrolytic methylation and compared for electron ionization and chemical ionization using several liquid reagents with increasing proton affinities. Electron ionization combined with pyrolysis caused extensive fragmentation, resulting in a high abundance of lower mass ions and diminishing the diagnostic value of the technique for compound identification and bacterial profiling. Chemical ionization reduced the amount of fragmentation due to ionization while enhancing the molecular ion region of the fatty acids. As the proton affinity of the reagent increased, the protonated molecular ions of the fatty acids became the predominant ions observed in the mass spectrum. As a result, chemical ionization was shown to be more effective than electron ionization in bacterial profiling. Whereas the bacteria could be distinguished at the Genera level using electron ionization, further differentiation to the subspecies level was possible using chemical ionization. The greatest separation among the five test organisms, in terms of Euclidean distances, was obtained using ethanol as the chemical ionization reagent and using pooled masses representing specific fatty acid biomarkers rather than total ion profiles.

Usefulness of pyrolysis coupled to gas chromatography/mass spectrometry for evaluating the reproducibility of commercial samples of Cymbopogon citratus Stapf., Poaceae

“…The range of applicability of the technique is illustrated by its use in the forensic field for the differentiation of paints (Kochanowski & Morgan, 2000;Zieba-Palus et al, 2008), analysis of whole organism in bacterial identification and classification (Barshick et al, 1999;Prasad et al, 2008) and analysis of vegetable material (Ibarra et al, 2007;Kim et al, 2003). The use of this technique in the analysis of herbal products has been very limited (Fang et al, 1990), but its potential is very promising.…”

Environmental Systems Research Candidates FY-01 Annual Report

“…28 Multivariate analyses have been successfully used for interpretation of mass spectra of microorganism-related chemistry. 29,30 After the initial attempts at principal components analysis (PCA), using grams/32 with the PLS/IQ package, we focused on finding the optimum mass ranges and optimum methodologies to design a methodology that for proof-of-principal could be used to classify bacteria based on their SIMS spectra. One problem has been that because the number of spectra is relatively limited for the calibration set (224) and the number of microbial types is large, there is currently no really good set of spectra to use as a verification set.…”

Characterisation of bacteria by matrix-assisted laser desorption/ionisation and electrospray mass spectrometry

“…This review gives an overview of the current possibilities of MS characterisation of bacteria with limitations posed by MS instrumentation and by the materials analysed. The scope of the review will be limited to the use of ES MS and MALDI MS. Characterisation of bacteria by pyrolysis MS is not discussed here, but the reader is referred to recent publications on this subject [13,14,15,16]. Characterisation by FAB MS of lipids is not discussed either; an excellent overview of this subject is already available [17].…”