The distribution of the known and putativevirulence related genes among Shigella spp. strains. The ORFs status is color-coded: blue, present/conserved; yellow, absent/divergent. The designations of these genes are indicated on the right. Strains are labelled according to the designations in Table 1. The product of stxA is shiga toxin. SigA and Pic are serine proteases. The gene clusters of iuc, iutA, iro, sit, shu, ent-fep, fhu, feo, tonB-exb, fec and SF1192-1194 are all iron acquisition associated. Two type II secretion systems are encoded by yhe and gsp respectively. The products of SDY0420-0424 are exoproteins.