Abstract
Pyrolysis mass spectrometry was used to produce
complex biochemical fingerprints of Eubacterium
exiguum, E. infirmum, E. tardum and E. timidum. To
examine the relationship between these organisms the
spectra were clustered by canonical variates analysis,
and four clusters, one for each species, were observed.
In an earlier study we trained artificial neural
networks to identify these clinical isolates
successfully; however, the information used by the
neural network was not accessible from this so-called
'black box' technique. To allow the deconvolution of
such complex spectra (in terms of which masses were
important for discrimination) it was necessary to
develop a system that itself produces 'rules' that are
readily comprehensible. We here exploit the
evolutionary computational technique of genetic
programming; this rapidly and automatically produced
simple mathematical functions that were also able to
classify organisms to each of the four bacterial groups
correctly and unambiguously. Since the rules used only
a very limited set of masses, from a search space some
50 orders of magnitude greater than the dimensionality
actually necessary, visual discrimination of the
organisms on the basis of these spectral masses alone
was also then possible.
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