Fig. 4

Virulence and fitness factors displaying variable gene content based on centroid-to-ortholog BSR. Specific genomic regions involved in the assembly of type I pili, siderophore production and efflux were highly variable and showed specific gain or loss of entire gene clusters in isolates analyzed. In the BSR-based heat map, the presence, absence, and low similarity of a protein ortholog compared with its centroid is shown in yellow (BSR = 1, presence), blue (BSR = 0, absence), and gray (low similarity or truncated), respectively. The year of collection is shown above strain names. Isolates collected prior to year 2000 are indicated with an asterisk. In summary, gene gain/loss events involved in virulence and survival were detected in decades-old isolates and appeared to have reemerged among recent isolates. The list of virulence genes analyzed and the full size version of the BSR-derived heat map are provided in Additional files 17 and 19, respectively