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the amount of a compound in a sample. This technique is widely used with
several modifications depending on the application.
Analysis of pathogenic and opportunistic free-living amoeba have been
successfully differentiated between using matrix-assisted laser desorption/
ionization mass spectrometry (MALDI-TOF MS) ( Fig. 8.2 ). Moura et al. 22
were able to generate 20 biomarker fingerprints for Acanthaamoeba , Balamuthia ,
and Naegleria fowleri with this method in less than 15min. The method was
extended by Donohue et al. 23 to describe the detection of the waterborne
pathogen Aeromonas , for which they found that the mass spectra data con-
tained enough information to distinguish between genera, species and strains.
The limitations of this method are that variations in culture conditions and
analytical parameters can significantly influence the mass spectra. The use of
this method for routine identification of pathogens from unknown samples
will require an extensive increase in the number and diversity of references
strains cataloged in the mass spectra library. 24
De Bruyne et al. 25 applied MALDI-TOF MS with machine learning
techniques (SVMs and RFs) to identify species within the genera Leu-
conostoc , Fructobacillus and Lactobacillus. The two machine learning tech-
niques improved the identification accuracy by 4-10%, to 94% and 98%
Figure 8.2 Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization tech-
nique used in mass spectrometry, allowing the analysis of biomolecules (such as pro-
teins, peptides, and sugars) and large organic molecules (such as polymers and other
macromolecules). The time of flight (TOF) method measures particle mass-to-charge
ratio by using an ion of known electrical charge and unknown mass, which enter a mass
spectrometer and are accelerated by an electrical field of known strength. This accelera-
tion results in any given ion having the same kinetic energy as any other ion given that
they all have the same charge. The velocity of the ion will depend, however, on the mass-
to-charge ratio as shown in the figure. Unknown ions can then be identified. Source:
Image taken from sigmaaldrich.com . http://www.bioacademy.gr/bioinformatics/courses/
Helsinki%207_11May07_projects/Introduction%20to%20Mass%20Spectrometry.pdf .
(For color version of this igure, the reader is referred to the online version of this topic.)
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