Considering the distribution of scores (Figure 1) and the distance relations between B. mallei and B. pseudomallei (Figure 5), this was not unexpected and obviously a consequence of the indiscriminate inclusion
of all available B. mallei and B. pseudomallei samples into the custom reference set. Classification could be substantially improved by selecting combinations of isolates of B. mallei and B. pseudomallei to form a dedicated reference set which is optimized for the discrimination of the two species. To screen the complete custom reference set of B. mallei and B. pseudomallei for appropriate combinations of isolates, the outcome of a database query was simulated with all permutations of up to four https://www.selleckchem.com/products/Adrucil(Fluorouracil).html members of each species. The smallest reference group yielding error-free results was composed of two B. mallei (M1, NCTC10247) and three B. pseudomallei (EF15660, PITT 225A, NCTC01688) isolates which are highlighted by an asterisk in Table 1. Not surprisingly, these isolates located close to the centers of their respective species in the Sammon plot visualization of the distance matrix (Figure 5). Finally, multivariate statistics on basis of the four different
statistical approaches (Genetic Algorithm, Support Vector Bortezomib Machine, Supervised Neural Network, Quick Classifier) available in ClinProTools 3.0 showed that B. mallei and B. pseudomallei could be well separated with cross validation results ranging between 98.95% and 100.00% (data not shown). Principal Component Analysis (PCA) carried out with ClinProTools 3.0 (Figure 6) further confirmed the separation of both species and also the broader distribution of B. pseudomallei in comparison with B. mallei. Figure 6 Principal component analysis of spectra derived from B. mallei and B. pseudomallei. Principle Component Analysis of ten strains of B. mallei and ten strains of B. pseudomallei, respectively. heptaminol The unsupervised statistical
analysis separates both species based on the three major principle components. While B. mallei form a relatively uniform cluster, significant diversity can be observed for B. pseudomallei. Analysis of the spectra from the specimens in Table 1 yielded very similar results (data not shown). Identification of taxon-specific biomarker ions Mass spectra of the reference spectrum set were analysed for species-specific masses which may be used for species identification independent of the score values considered so far. For that purpose the mass lists of the MSP generated with MALDI Biotyper software were evaluated in detail. An alignment of all masses occurring in the spectra was constructed as a table in which every column represented the mass spectrum of a sample and every row the intensity of a mass occurring in a certain mass range. The alignment contained a total of 350 masses.