Discriminating patients with S aureus infections from patients with E coli infections. (A) Hierarchical clustering of 211 genes obtained from Mann-Whitney rank test comparison (P < .01) between 2 groups: Staphylococcus aureus (S aureus, 10 samples, red rectangle) and Escherichia coli (E coli, 10 samples, blue rectangle) infections. Transformed expression levels are indicated by color scale, with red representing relative high expression and blue indicating relative low expression compared to the median expression for each gene across all donors. Genes are listed in Table S4. (B) A supervised learning algorithm was used to identify 30 genes presenting the highest capacity to discriminate the 2 classes (Table S6). Leave-one-out cross-validation of the training set with 30 classifier genes grouped the samples with 95% accuracy. (C) The 30 classifier genes thus identified were tested on an independent set of patients (open rectangles), including 21 new patients with S aureus and 19 with E coli infections. The 40 samples in this test set were predicted with 85% accuracy (predicted class is indicated by light-colored rectangles). Of these 40 samples, only 2 were misclassified, whereas the class of 4 other samples could not be determined (open rectangles).